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| {{redirect|Four|other uses|4 (disambiguation)}}
| | Roberto is the name Method love to be known with although it can be not the name to do with my birth certificate. I am a cashier. My your friends say it's not wonderful for me but what I love doing should be to drive but I do have been taking on new things lately. My house is but in [http://Www.alexa.com/search?q=Vermont&r=topsites_index&p=bigtop Vermont]. I've been working on particular website for some period now. Check it out side here: http://prometeu.net<br><br>Here is my site; [http://prometeu.net clash of clans trucos gemas] |
| {{example farm|date=March 2010}}
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| {{Infobox number
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| | number = 4
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| | numeral = [[Quaternary numeral system|quaternary]]
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| | divisor = 1, 2, 4
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| | roman unicode = Ⅳ, ⅳ
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| | greek prefix = [[wikt:tetra-|tetra-]]
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| | latin prefix = [[wikt:quadri-|quadri-]]/[[wikt:quadr-|quadr-]]
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| | lang1 = [[Greek numerals|Greek]]
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| | lang1 symbol = δ (or Δ)
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| | lang2 = [[Arabic language|Arabic]]
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| | lang2 symbol = {{resize|150%|٤,4}}
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| | lang3 = [[Persian language|Persian]]
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| | lang3 symbol = {{resize|150%|۴}}
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| | lang4 = [[Urdu]]
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| | lang4 symbol= {{Urdu numeral|4|20}}
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| | lang5 = [[Ge'ez alphabet|Ge'ez]]
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| | lang5 symbol = ፬
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| | lang6 = [[Bengali language|Bengali]]
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| | lang6 symbol = {{resize|150%|৪}}
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| | lang7 = [[Chinese numeral]]
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| | lang7 symbol = 四，亖，肆
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| | lang8 = [[Korean numerals|Korean]]
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| | lang8 symbol = 넷,사
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| | lang9 = [[Devanāgarī|Devanagari]]
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| | lang9 symbol = {{resize|150%|४}} (char)
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| | lang10 = [[Telugu language|Telugu]]
| |
| | lang10 symbol = {{resize|150%|౪}}
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| | lang11 = [[Malayalam Language|Malayalam]]
| |
| | lang11 symbol = {{resize|150%|൪}}
| |
| | lang12 = [[Tamil language|Tamil]]
| |
| | lang12 symbol = {{resize|150%|௪}}
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| | lang13 = [[Hebrew (language)|Hebrew]]
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| | lang13 symbol = ארבע (Arba, pronounced AR-bah) or {{resize|150%|ד}} ([[Dalet]], 4th letter of the Hebrew alphabet)
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| | lang14 = [[Khmer numerals|Khmer]]
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| | lang14 symbol = ៤
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| | lang15 = [[Thai numerals|Thai]]
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| | lang15 symbol = ๔
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| | lang16 = [[Kannada language|Kannada]]
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| | lang16 symbol = ४
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| }}
| |
| '''4''' ('''four'''; {{IPAc-en|'|f|oUr}}) is a [[number]], [[numeral system|numeral]], and [[glyph]]. It is the [[natural number]] following {{num|3}} and preceding {{num|5}}. Four is the only number that has the same number of characters as its value in the English language.<ref>{{cite web|url=http://www.omg-facts.com/view/Facts/3109|title=Four facts about 4|publisher=Omg facts}}</ref>
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| | |
| ==In mathematics==
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| Four is the smallest [[composite number]], its proper [[divisor]]s being {{num|1}} and {{num|2}}. Four is also a [[highly composite number]]. The next highly composite number is {{num|6}}.
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| | |
| Four is the second [[square number]], the second [[centered triangular number]].
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| | |
| 4 is the smallest squared prime (''p''<sup>2</sup>) and the only even number in this form. It has an [[aliquot sum]] of 3 which is itself prime. The [[aliquot sequence]] of 4 has 4 members (4, {{num|3}}, 1, 0) and is accordingly the first member of the 3-aliquot tree.
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| | |
| A number is a multiple of 4 if its last two digits are a multiple of 4. For example, 1092 is a multiple of 4 because 92 = 4×23.
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| | |
| Only one number has an aliquot sum of 4 and that is squared prime {{num|9}}.
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| | |
| The prime factorization of four is two times two.
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| | |
| Four is the smallest composite number that is equal to the sum of its prime factors. (As a consequence of this, it is the smallest [[Smith number]]). However, it is the only composite number ''n'' for which <math>(n - 1)!\ \equiv\ 0 \ ({\rm mod}\ n)</math> is false.
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| | |
| It is also a [[Motzkin number]].
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| | |
| In bases 6 and 12, 4 is a 1-[[automorphic number]].
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| | |
| In addition, 2 + 2 = 2 × 2 = 2<sup>2</sup> = 4. Continuing the pattern in [[Knuth's up-arrow notation]], <math>2 \uparrow\uparrow 2 = 2 \uparrow\uparrow\uparrow 2 = 4</math>, and so on, for any number of up arrows.
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| | |
| A four-sided plane figure is a [[quadrilateral]] (quadrangle) or [[square (geometry)|square]], sometimes also called a ''tetragon''. A [[circle]] divided by 4 makes [[right angle]]s. Because of it, four (4) is the base number of [[plane (mathematics)]]. Four [[cardinal directions]], [[Season|four seasons]], [[duodecimal]] system, and [[vigesimal]] system are based on four.
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| | |
| A solid figure with four faces is a [[tetrahedron]]. The regular tetrahedron is the simplest [[Platonic solid]]. A [[tetrahedron]], which can also be called a 3-[[simplex]], has four triangular faces and four vertices. It is the only self-dual [[regular polyhedron]].
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| | |
| [[Four-dimensional space|Four-dimensional]] space is the highest-dimensional space featuring more than three convex regular figures:
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| * Two-dimensional: infinitely many convex [[regular polygon]]s.
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| * Three-dimensional: five convex [[Regular polyhedron|regular polyhedra]] (the five [[Platonic Solid]]s).
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| * Four-dimensional: six [[Convex regular 4-polytope|convex regular polychora]].
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| * Five-dimensional and every higher-dimensional: three regular convex [[polytope]]s ([[simplex|regular simplexes]], [[hypercube]]s, [[cross-polytope]]s).
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| | |
| Four-dimensional [[differential manifold]]s have some unique properties. There is only one [[differential structure]] on <math>\mathbb{R}^{n}</math> except when ''n'' = 4, in which case there are uncountably many.
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| | |
| The smallest non-[[cyclic group|cyclic]] [[group (mathematics)|group]] has four elements; it is the [[Klein four-group]]. Four is also the order of the smallest non-trivial groups that are not [[simple group|simple]].
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| | |
| Four is the maximum number of dimensions of a real [[division algebra]] (the [[quaternions]]), by a theorem of [[Ferdinand Georg Frobenius]].
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| | |
| The [[four-color theorem]] states that a [[planar graph]] (or, equivalently, a flat [[map]] of two-dimensional regions such as countries) can be colored using four colors, so that adjacent vertices (or regions) are always different colors.<ref>Bryan Bunch, ''The Kingdom of Infinite Number''. New York: W. H. Freeman & Company (2000): 48</ref> Three colors are not, in general, sufficient to guarantee this. The largest planar [[complete graph]] has four vertices.
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| | |
| [[Lagrange's four-square theorem]] states that every positive integer can be written as the sum of at most four [[square number]]s. Three are not always sufficient; {{num|7}} for instance cannot be written as the sum of three squares.
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| Four is the first positive non-[[Fibonacci number]].
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| Each natural number divisible by 4 is a difference of squares of two natural numbers, i.e. 4''x'' = ''y''<sup>2</sup> − ''z''<sup>2</sup>.
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| Four is an [[Harshad number|all-Harshad number]] and a [[semi-meandric number]].
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| | |
| ===List of basic calculations===
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| {|class="wikitable" style="text-align: center; background: white"
| |
| |-
| |
| !width="105px"|[[Multiplication]]
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| !1
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| !2
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| !3
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| !4
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| !5
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| !6
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| !7
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| !8
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| !9
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| !10
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| !width="5px"|
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| !11
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| !12
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| !13
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| !14
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| !15
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| !16
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| !17
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| !18
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| !19
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| !20
| |
| !width="5px"|
| |
| !21
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| !22
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| !23
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| !24
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| !25
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| !width="5px"|
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| !50
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| !100
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| !1000
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| |-
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| |<math>4 \times x</math>
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| |'''4'''
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| |{{num|8}}
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| |{{num|12}}
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| |{{num|16}}
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| |{{num|20}}
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| |{{num|24}}
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| |{{num|28}}
| |
| |{{num|32}}
| |
| |{{num|36}}
| |
| |{{num|40}}
| |
| !
| |
| |{{num|44}}
| |
| |{{num|48}}
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| |{{num|52}}
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| |{{num|56}}
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| |{{num|60}}
| |
| |{{num|64}}
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| |{{num|68}}
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| |{{num|72}}
| |
| |{{num|76}}
| |
| |{{num|80}}
| |
| !
| |
| |{{num|84}}
| |
| |{{num|88}}
| |
| |{{num|92}}
| |
| |{{num|96}}
| |
| |{{num|100}}
| |
| !
| |
| |{{num|200}}
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| |{{num|400}}
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| |{{num|4000}}
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| |}
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| {|class="wikitable" style="text-align: center; background: white"
| |
| |-
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| !width="105px"|[[Division (mathematics)|Division]]
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| !1
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| !2
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| !3
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| !4
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| !5
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| !6
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| !7
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| !8
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| !9
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| !10
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| !width="5px"|
| |
| !11
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| !12
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| !13
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| !14
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| !15
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| !16
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| |-
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| |<math>4 \div x</math>
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| |'''4'''
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| |2
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| |<math>1.\overline{3}</math>
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| |1
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| |0.8
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| |<math>0.\overline{6}</math>
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| |<math>0.\overline{571428}</math>
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| |0.5
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| |<math>0.\overline{4}</math>
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| |0.4
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| !
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| |<math>0.\overline{36}</math>
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| |<math>0.\overline{3}</math>
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| |<math>0.\overline{307692}</math>
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| |<math>0.\overline{285714}</math>
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| |<math>0.2\overline{6}</math>
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| |0.25
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| |-
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| |<math>x \div 4</math>
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| |0.25
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| |0.5
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| |0.75
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| |1
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| |1.25
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| |1.5
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| |1.75
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| |2
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| |2.25
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| |2.5
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| !
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| |2.75
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| |3
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| |3.25
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| |3.5
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| |3.75
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| |4
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| |}
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| | |
| {|class="wikitable" style="text-align: center; background: white"
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| |-
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| !width="105px"|[[Exponentiation]]
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| !1
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| !2
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| !3
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| !4
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| !5
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| !6
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| !7
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| !8
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| !9
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| !10
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| !width="5px"|
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| !11
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| !12
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| !13
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| |-
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| |<math>4 ^ x\,</math>
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| |4
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| |16
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| |64
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| |256
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| |1024
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| |4096
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| |16384
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| |65536
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| |262144
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| |1048576
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| !
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| |4194304
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| |16777216
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| |67108864
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| |-
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| |<math>x ^ 4\,</math>
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| |1
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| |16
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| |81
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| |256
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| |625
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| |1296
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| |2401
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| |4096
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| |6561
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| |10000
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| !
| |
| |14641
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| |20736
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| |28561
| |
| |}
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| | |
| ==Evolution of the glyph==
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| [[File:Evolution4glyph.png|x50px|right]]
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| Representing 1, 2 and 3 in as many lines as the number represented worked well. The [[Brahmin]] Indians simplified 4 by joining its four lines into a cross that looks like our modern plus sign. The [[Sunga empire|Sunga]] would add a horizontal line on top of the numeral, and the Kshatrapa and Pallava evolved the numeral to a point where speed of writing was a secondary concern. The [[Arab]]s' 4 still had the early concept of the cross, but for the sake of efficiency, was made in one stroke by connecting the "western" end to the "northern" end; the "eastern" end was finished off with a curve. The Europeans dropped the finishing curve and gradually made the numeral less cursive, ending up with a glyph very close to the original Brahmin cross.<ref>Georges Ifrah, ''The Universal History of Numbers: From Prehistory to the Invention of the Computer'' transl. David Bellos et al. London: The Harvill Press (1998): 394, Fig. 24.64</ref>
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| While the shape of the 4 character has an [[ascender (typography)|ascender]] in most modern [[typeface]]s, in typefaces with [[text figures]] the character usually has a [[descender]], as, for example, in [[File:TextFigs148.svg|40px]].
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| [[File:Seven-segment 4.svg|x50px|left]]
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| On the [[seven-segment display]]s of pocket calculators and digital watches, as well as certain [[optical character recognition]] fonts, 4 is seen with an open top.
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| [[Television station]]s that operate on [[channel 4 (disambiguation)|channel 4]] have occasionally made use of another variation of the "open 4", with the open portion being on the side, rather than the top. This version resembles the [[Canadian Aboriginal syllabics]] letter ᔦ. The [[magnetic ink character recognition]] "CMC-7" font also uses this variety of "4".
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| ==In religion==
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| ;Buddhism
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| * [[Four Noble Truths]]
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| ** [[Dukkha]] – The Noble Truth of Suffering
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| ** [[Pratītyasamutpāda|Samudaya]] – The Noble Truth of the Cause of Suffering
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| ** [[Nirvana|Nirodha]] – The Noble Truth of the Cessation of Suffering
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| ** [[Noble Eightfold Path|Magga]] – The Noble Truth of the Path leading to the Cessation of Suffering
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| * [[Four sights]] – observations which affected Prince Siddhartha deeply and made him realize the sufferings of all beings, and compelled him to begin his spiritual journey—an [[old age|old]] man, a [[illness|sick]] man, a [[death|dead]] man, and an [[ascetic]]
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| * [[Mahābhūta|Four Great Elements]] – [[earth (classical element)|earth]], [[water (classical element)|water]], [[fire (classical element)|fire]], and [[air (classical element)|wind]]
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| * [[Four Heavenly Kings]]
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| * [[Satipatthana|Four Foundations of Mindfulness]] – contemplation of the body, contemplation of feelings, contemplation of mind, contemplation of mental objects
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| * [[Four Right Exertions]]
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| * [[Iddhipada|Four Bases of Power]]
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| * [[Jhāna|Four jhānas]]
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| * [[Arūpajhāna|Four arūpajhānas]]
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| * [[Brahmavihara|Four Divine Abidings]] – [[Mettā|loving-kindness]], [[Karuṇā|compassion]], [[Mudita|sympathetic joy]], and [[Upekkha|equanimity]]
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| * [[Four stages of enlightenment]] – [[Sotāpanna|stream-enterer]], [[Sakadagami|once-returner]], [[Anagami|non-returner]], and [[Arahant (Buddhism)|arahant]]
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| * [[Buddhist pilgrimage|Four main pilgrimage sites]] – [[Lumbini]], [[Bodh Gaya]], [[Sarnath]], and [[Kusinara]]
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| ;Judeo-Christian symbolism
| |
| * The [[Tetragrammaton]] is the four-letter name of [[God]].
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| * The four Matriarchs (foremothers) of [[Judaism]] are [[Sarah]], [[Rebekah]], [[Leah]], and [[Rachel]].
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| * The [[Four Species]] ([[lulav]], [[hadass]], [[Aravah (Sukkot)|aravah]] and [[etrog]]) are taken as one of the [[mitzvah|mitzvot]] on the [[Jewish]] holiday of [[Sukkot]]. ([[Judaism]])
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| * The Four Cups of Wine to drink on the [[Jewish]] holiday of [[Passover]]. ([[Judaism]])
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| * The Four Questions to be asked on the [[Jewish]] holiday of [[Passover]]. ([[Judaism]])
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| * The Four Sons to be dealt with on the [[Jewish]] holiday of [[Passover]]. ([[Judaism]])
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| * The Four Expressions of Redemption to be said on the [[Jewish]] holiday of [[Passover]]. ([[Judaism]])
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| * The [[Four Horsemen of the Apocalypse]] ride in the [[Book of Revelation]].
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| * The four [[Gospel]]s: [[Gospel of Matthew|Matthew]], [[Gospel of Mark|Mark]], [[Gospel of Luke|Luke]], and [[Gospel of John|John]].
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| ;Hinduism
| |
| * In [[Puruṣārtha]] there are 4 aims of human life [[Dharma]], [[Artha]], [[Kāma]], [[Moksha]].
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| * The four stages of life [[Brahmacharya]] (student life), [[Grihastha]] (household life), [[Vanaprastha]] (retired life) and [[Sannyasa]] (renunciation).
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| * The four primary castes or strata of society [[Brahmana]] (priest/teacher), [[Kshatriya]] (warrior/politician), [[Vaishya]] (landowner/entrepreneur) and [[Shudra]] (servant/manual laborer).
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| ;Islam
| |
| * [[Eid al-Adha]] lasts for four days, from the 10th to the 14th of [[Dhul Hijja]].
| |
| * There are four The Rightly Guided Caliphs or [[Rashidun]]: [[Abu Bakr]], [[Umar ibn al-Khattab]], [[Uthman ibn Affan]] and [[Ali ibn Abi Talib]].
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| * The Four Arch Angels in Islam are: Jibraeel (Gabriel), Mikaeel (Michael), Izraeel (Azrael), and Israfil (Raphael)
| |
| * There are four Sacred Months in Islam: [[Muharram]], [[Rajab]], [[Dhu al-Qi'dah]] and [[Dhu al-Hijjah]].
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| * There are four [[Sunni]] schools of [[fiqh]]: [[Hanafi]], [[Shafi`i]], [[Maliki]] and [[Hanbali]].
| |
| * There are four major sunni Imams: [[Abū Ḥanīfa]], [[Muhammad ibn Idris ash-Shafi`i]], [[Malik ibn Anas]] and [[Ahmad ibn Hanbal]].
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| * There are four books in Islam: Torah, Zaboor, Injeel, Quran.
| |
| * Waiting for four months is ordained for those who take an oath for abstention from their wives.
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| * The waiting period of the woman whose husband dies, is four months and ten days.
| |
| * When Abraham said: “My Lord, show me how You give life to the dead,” Allah said: “Why! Do you have no faith?” Abraham replied: “Yes, but in order that my heart be at rest.” He said: “Then take four birds, and tame them to yourself, then put a part of them on every hill, and summon them; they will come to you flying.
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| * The respite of four months was granted to give time to the mushriks in Surah Taubah so that they should consider their position carefully and decide whether to make preparation for war or to emigrate from the country or to accept Islam.
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| * Those who accuse honourable women (of unchastity) but do not produce four witnesses, flog them with eighty lashes, and do not admit their testimony ever after. They are indeed transgressors.
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| ;Other
| |
| * Four is the sacred number of the [[Zia (New Mexico)|Zia]], an indigenous tribe located in the [[U.S.]] State of [[New Mexico]].
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| * The Chinese, Vietnamese, the Korean and the Japanese are [[tetraphobia|superstitious about the number four]] because it is a homonym for "death" in their languages.
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| | |
| ==In science==
| |
| * A [[tetramer]] is a thing formed out of four sub-units.
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| | |
| ===In astronomy===
| |
| * Four terrestrial (or rocky) planets in the [[Solar system]]: [[Mercury (planet)|Mercury]], [[Venus]], [[Earth]], [[Mars]].
| |
| * Four giant gas planets in the [[Solar system]]: [[Jupiter]], [[Saturn]], [[Uranus]], [[Neptune]].
| |
| * Four of Jupiter's moons (the [[Galilean moons]]) are readily visible from Earth.
| |
| * [[Messier object]] [[Messier 4|M4]], a magnitude 7.5 [[globular cluster]] in the constellation [[Scorpius]].
| |
| * The [[New General Catalogue]] [http://www.ngcic.org/ object] [[NGC 4]], a faint [[galaxy]] in the [[constellation]] [[Pisces (constellation)|Pisces]]
| |
| * The Roman numeral IV stands for [[subgiant]] in the [[stellar classification|Yerkes spectral classification scheme]].
| |
| * The Roman numeral IV (usually) stands for the fourth-discovered satellite of a planet or minor planet (e.g. [[Jupiter IV]])
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| | |
| ===In biology===
| |
| * Four is the number of [[nucleobase]] types in [[DNA]] and [[RNA]] – [[adenine]], [[guanine]], [[cytosine]], [[thymine]] ([[uracil]] in [[RNA]]).
| |
| * Many [[chordate]]s have four feet, legs or leglike appendages ([[Tetrapods]]).
| |
| * The [[mammal]]ian [[heart]] consists of four chambers.
| |
| * Many [[mammal]]s ([[Carnivora]], [[Ungulata]]) use four fingers for movement.
| |
| * The fourth finger of a human hand (on the left hand – ring-finger) is moved when the little finger moves.
| |
| * All [[insect]]s with wings except [[fly|flies]] have four [[wing]]s.
| |
| * Insects of the superorder [[Endopterygota]], also known as Holometabola, such as butterflies, ants, bees, beetles, fleas, flies, moths, and wasps, undergo [[holometabolism]] – complete metamorphism in four stages – from (1) embryo (ovum, egg), to (2) larva (such as grub, caterpillar), then (3) pupa (such as the chrysalis), and finally (4) the imago.
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| * There are four human [[blood]] groups (A, B, O, AB).
| |
| * [[Humans]] have four [[canine tooth|canines]], four [[incisor]]s and four [[wisdom teeth]].
| |
| * The cow's stomach is divided in four digestive compartments: reticulum, rumen, omasum and abomasum.
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| | |
| ===In chemistry===
| |
| * [[Valence (chemistry)|Valency]] of [[carbon]] (that is basis of life on the Earth) is four. Also because of its tetrahedral crystal bond structure, [[diamond]] (one of the natural allotropes of carbon) is the hardest known naturally occurring material. It is also the valence of [[silicon]], whose compounds form the majority of the mass of the Earth's crust.
| |
| * The [[atomic number]] of [[beryllium]]
| |
| * There are four basic states of [[matter]]: [[solid]], [[liquid]], [[gas]], and [[plasma (physics)|plasma]].
| |
| * The four elements of [[alchemy]] are [[earth]], [[water]], [[air]] and [[fire]].
| |
| | |
| ===In physics===
| |
| * [[Special relativity]] and [[general relativity]] treat nature as four-[[dimension]]al – [[time]] and three-dimensional [[space]] are treated together and called [[spacetime]]. Also, any event ''E'' has a [[light cone]] composed of four zones of possible communication and cause and effect (outside the light cone is strictly incommunicado).
| |
| * An [[alpha particle]] (helium nucleus, also called a helion) consists of four [[hadron]]s.
| |
| * There are four [[fundamental forces]] ([[electromagnetism]], [[gravitation]], the [[weak nuclear force]], and the [[strong nuclear force]]).
| |
| * In [[statistical mechanics]], the [[four functions inequality]] is an inequality for four functions on a finite [[distributive lattice]].
| |
| | |
| ==In logic and philosophy==
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| * The symbolic meanings of the number four are linked to those of the cross and the square. "Almost from prehistoric times, the number four was employed to signify what was solid, what could be touched and felt. Its relationship to the cross (four points) made it an outstanding symbol of wholeness and universality, a symbol which drew all to itself". Where lines of latitude and longitude intersect, they divide the earth into four proportions. Throughout the world kings and chieftains have been called "lord of the four suns"..."lord of the four quarters of the earth"...<ref><span lang=fr>Chevalier, Jean</span> and <span lang=fr>Gheerbrant, Alain</span> (1994), ''The Dictionary of Symbols''. The quote beginning "Almost from prehistoric times..." is on p. 402.</ref> by which is understood to the extent of their powers both territorially and in terms of total control of their subjects' doings.
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| * The [[Square of Opposition]], in both its Aristotelian version and its [[Square of Opposition#Modern squares of opposition|Boolean version]], consists of four forms: A ("All ''S'' is ''R''"), I ("Some ''S'' is ''R''"), E ("No ''S'' is ''R''"), and O ("Some ''S'' is not ''R''").
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| * In regard to whether two given propositions can have the same [[truth value]], there are four separate logical possibilities: the propositions are ''subalterns'' (possibly both are true, and possibly both are false); ''subcontraries'' (it is possible that both are true, but not that both are false); ''contraries'' (it is possible that both are false, but not that both are true); or ''contradictories'' (it is not possible that both are true, and it is not possible that both are false).
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| * [[Aristotle]] held that there are basically [[Aristotle#Causality, the four causes|four causes]] in nature: the [[Four causes#Efficient cause|efficient cause]], the [[Four causes#Material cause|matter]], the [[Four causes#Final cause|end]], and the [[Four causes#Formal cause|form]].
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| * The [[Stoicism|Stoics]] held with four basic [[categories (Stoic)|categories]], all viewed as bodies (substantial and insubstantial): (1) ''substance'' in the sense of substrate, primary formless matter; (2) ''quality'', matter's organization to differentiate and individualize something, and coming down to a physical ingredient such as ''pneuma'', breath; (3) ''somehow holding'' (or ''disposed''), as in a posture, state, shape, size, action, and (4) ''somehow holding'' (or ''disposed'') ''toward something,'' as in relative location, familial relation, and so forth.
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| * [[Immanuel Kant]] expounded a [[Category (Kant)#The table of judgments|table of judgments]] involving four three-way alternatives, in regard to (1) Quantity, (2) Quality, (3) Relation, (4) Modality, and, based thereupon, a [[Category (Kant)#The table of categories|table of four categories]], named by the terms just listed, and each with three subcategories.
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| * [[Arthur Schopenhauer]]'s doctoral thesis was ''[[On the Fourfold Root of the Principle of Sufficient Reason]]''.
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| * [[Franz Brentano]] held that any major philosophical period has four phases: (1) Creative and rapidly progressing with scientific interest and results; then declining through the remaining phases, (2) practical, (3) increasingly skeptical, and (4) literary, mystical, and scientifically worthless – until philosophy is renewed through a new period's first phase. (See Brentano's essay "The Four Phases of Philosophy and Its Current State" 1895, tr. by Mezei and Smith 1998.)
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| * [[Charles Sanders Peirce|C. S. Peirce]], usually a [[trichotomy (philosophy)|trichotomist]], discussed four methods for overcoming troublesome uncertainties and achieving secure beliefs: (1) the method of tenacity (policy of sticking to initial belief), (2) the method of authority, (3) the method of congruity (following a fashionable [[paradigm]]), and (4) the [[Fallibilism|fallibilistic]], self-correcting method of science (see "[[s:The Fixation of Belief|The Fixation of Belief]]", 1877); and four barriers to inquiry, barriers refused by the fallibilist: (1) assertion of absolute certainty; (2) maintaining that something is absolutely unknowable; (3) maintaining that something is absolutely inexplicable because absolutely basic or ultimate; (4) holding that perfect exactitude is possible, especially such as to quite preclude unusual and anomalous phenomena (see "[http://www.princeton.edu/~batke/peirce/frl_99.htm F.R.L.]" [First Rule of Logic], 1899).
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| * [[Paul Weiss (philosopher)|Paul Weiss]] built a system involving four modes of being: Actualities (substances in the sense of substantial, spatio-temporally finite beings), Ideality or Possibility (pure normative form), Existence (the dynamic field), and God (unity). (See Weiss's ''Modes of Being'', 1958).
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| * [[Karl Popper]] outlined a tetradic schema to describe the growth of theories and, via generalization, also the emergence of new behaviors and living organisms: (1) problem, (2) tentative theory, (3) (attempted) error-elimination (especially by way of critical discussion), and (4) new problem(s). (See Popper's ''Objective Knowledge'', 1972, revised 1979.)
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| * [[John Boyd (military strategist)]] made his key concept the decision cycle or [[John Boyd (military strategist)#The OODA Loop|OODA loop]], consisting of four stages: (1) observation (data intake through the senses), (2) orientation (analysis and synthesis of data), (3) decision, and (4) action. Boyd held that his decision cycle has philosophical generality, though for strategists the point remains that, through swift decisions, one can disrupt an opponent's decision cycle.
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| * [[Richard McKeon]] outlined four classes (each with four subclasses) of modes of philosophical inquiry: (1) Modes of Being (Being); (2) Modes of Thought (That which is); (3) Modes of Fact (Existence); (4) Modes of Simplicity (Experience) – and, corresponding to them, four classes (each with four subclasses) of philosophical semantics: Principles, Methods, Interpretations, and Selections. (See McKeon's "Philosophic Semantics and Philosophic Inquiry" in ''Freedom and History and Other Essays'', 1989.)
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| * [[Jonathan Lowe]] (E.J. Lowe) argues in ''The Four-Category Ontology,'' 2006, for four categories: ''kinds'' (substantial universals), ''attributes'' (relational universals and property-universals), ''objects'' (substantial particulars), and ''modes'' (relational particulars and property-particulars, also known as "[[trope (philosophy)|tropes]]"). (See Lowe's "Recent Advances in Metaphysics," 2001, [http://www.cs.vassar.edu/~weltyc/fois/fois-2001/keynote/ Eprint])
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| ==In technology== | |
| [[File:U+2676 DejaVu Sans.svg|50px|right|4 as a resin identification code, used in recycling.]]
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| * The [[resin identification code]] used in recycling to identify [[low-density polyethylene]].
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| * Most [[furniture]] has four legs – tables, chairs, etc.
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| * Four [[horse]]s (quadriga) is the maximal number of horses in one row for carriage.
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| * The [[four color process]] ([[CMYK]]) is used for [[printing]].
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| * Wide use of [[rectangle]]s (with four angles and four sides) because they have effective form and capability for close adjacency to each other (houses, rooms, tables, bricks, sheets of paper, screens, film frames).
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| * In the [[Rich Text Format]] specification, language code 4 is for the [[Chinese language]]. Codes for regional variants of Chinese are congruent to 4 mod 256.
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| * [[Credit card]] machines have four-twelve function keys.
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| * On most phones, the 4 key is associated with the letters [[G]], [[H]], and [[I]], but on the [[BlackBerry]] cellular phone, it is the key for [[D]] and [[F]].
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| * On many [[computer keyboard]]s, the "4" key may also be used to type the [[dollar sign]] ($) if the [[shift key]] is held down.
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| * It is the number of [[bit]]s in a [[nibble]], equivalent to half a [[byte]]
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| * In [[internet slang]], "4" can replace the word "for" (as "four" and "for" are pronounced similarly). For example, typing "4u" instead of "for you".
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| * In [[Leet]]speak, "4" may be used to replace the letter "A".
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| ==In transport==
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| [[File:BKV m 4 jms.svg|100px|right]]
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| * Most [[vehicle]]s, including [[motor vehicle]]s, and particularly [[automobile|cars/automobiles]] and light [[commercial vehicle]]s have four road [[wheel]]s.
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| * "[[quattro (four wheel drive system)|quattro]]", meaning four in the Italian language, is used by [[Audi]] as a trademark to indicate that [[four-wheel drive]] (4WD) technologies are used on Audi-branded cars. The word "Quattro" was initially used by Audi in 1980 in its original 4WD coupé, the [[Audi Quattro]]. Audi also has a privately held subsidiary company called [[quattro GmbH]].
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| * [[List of highways numbered 4]]
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| ==In sports==
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| * In [[cricket]], a four is a specific type of scoring event, whereby the ball crosses the [[boundary (cricket)|boundary]] after touching the ground at least one time, scoring four runs. Taking four wickets in four consecutive balls is typically referred to as a double hat trick (two consecutive, overlapping hat tricks).
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| * In [[basketball]], the number four is used to designate the [[Power Forward (basketball)|Power Forward]] position, often referred to as "The four spot".
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| * Also in [[basketball]], there is a term called the [[four point play]], when a fouled player attempts a [[3-point field goal]] and makes it, and makes the resulting [[free throw]].
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| * The number of quarters in an [[NBA]] or [[NFL]] game.
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| * The basketball term [[Final Four]] refers to:
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| ** in the United States, the last four teams remaining in the NCAA playoff tournament, each of which is the winner of its respective region (for collegiate hockey the term [[Frozen Four]] is used).
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| ** In Europe, the last four teams remaining in many national and transnational club competitions, most notably the [[Euroleague Basketball|Euroleague]].
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| * In [[rowing (sport)|rowing]], a four refers to a [[boat]] for four rowers, with or without [[coxswain]]. In rowing nomenclature 4− represents a coxless four and 4+ represents a coxed four.
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| * There are four bases in the game of [[baseball]]: [[first base]], [[second base]], [[third base]], and [[home plate]]; to score a run, an offensive player must complete, in the sequence shown, a circuit of those four bases.
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| * In [[baseball]] scoring, number 4 is assigned to the [[second baseman]]. Also, four is the most number of runs that can be scored on any single at bat, whereby all three baserunners and the batter score (the most common being via a [[grand slam (baseball)|grand slam]]).
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| * In [[gridiron football]] codes,
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| ** In [[American football]], the offensive team has four downs (plays) to advance the ball 10 yards otherwise loss of possession occurs.
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| ** four points are awarded in a handful of leagues for rarely attempted types of [[field goal (American football)|field goals]]; an example is in [[six-man football]]. Because of the difficulties of getting a successful kick due to the few players on the field, a field goal is worth four points. Also, in [[Arena Football]], a successful [[dropkick]]ed field goal attempt scores four points.
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| ** the "four hole" in offense terminology is the space between the right guard and the right tackle on the offensive line
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| ** the "four back" is an extra [[running back]] (outside the [[fullback (American football)|fullback]] and [[halfback (American football)|halfback]], often referred to as an [[H-back]]) in the backfield; e.g. a play call for a "44 lead" indicates the H-back will follow the fullback into the hole between the right guard and the right tackle.
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| * In [[rugby union]]:
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| ** One of the two starting [[Lock (rugby union)|locks]] wears the jersey number 4.
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| ** At several points in the history of the sport, 4 points were awarded for the following scores:
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| *** A [[goal from mark]] from 1891 to 1904 (3 points after that time; abolished in 1977).
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| *** A [[drop goal]] from 1891 to 1947 (now 3 points).
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| *** A [[try]] from 1971 to 1991 (now 5 points).
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| ** In most league competitions, as well as the pool phases of the [[Rugby World Cup]] and many other worldwide championships, 4 competition points are awarded for a win (see [[rugby union bonus points system]]).
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| * In [[rugby league]]:
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| ** A try is worth 4 points.
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| ** In most competitions (though not the European [[Super League]], which uses static squad numbering), the starting [[Rugby league positions#Centres|left centre]] wears jersey number 4.
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| * The jersey number 4 has been retired by several [[Major professional sports leagues in the United States and Canada|North American sports]] teams in honor of past playing greats or other key figures:
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| ** In [[Major League Baseball]]:
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| *** The [[Baltimore Orioles]], for [[National Baseball Hall of Fame and Museum|Hall of Fame]] [[manager (baseball)|manager]] [[Earl Weaver]].
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| *** The [[Boston Red Sox]], for Hall of Famer [[Joe Cronin]].
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| *** The [[Chicago White Sox]], for Hall of Famer [[Luke Appling]].
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| *** The [[Los Angeles Dodgers]], for Hall of Famer [[Duke Snider]].
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| *** The [[Milwaukee Brewers]], for Hall of Famer [[Paul Molitor]].
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| *** The [[History of the New York Giants (NL)|New York Giants]], for Hall of Famer [[Mel Ott]]; the team has continued to honor the number in its current home of [[San Francisco Giants|San Francisco]].
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| *** The [[New York Yankees]], for Hall of Famer [[Lou Gehrig]]. Notably, he was the first player in major North American sports to be so honored by a U.S.-based team (he was preceded in this honor by [[Ace Bailey]], whose [[6 (number)#In sports|#6]] was retired by the Toronto Maple Leafs five years earlier).
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| *** The [[Pittsburgh Pirates]], for Hall of Famer [[Ralph Kiner]].
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| ** In the [[National Basketball Association|NBA]]:
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| *** The [[Chicago Bulls]], for [[Jerry Sloan]], who later served as the team's head coach and went on to a [[Naismith Memorial Basketball Hall of Fame|Hall of Fame]] career [[List of coaches in the Naismith Memorial Basketball Hall of Fame|in that role]] (mainly with the [[Utah Jazz]]).
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| *** The [[Detroit Pistons]], for [[List of players in the Naismith Memorial Basketball Hall of Fame|Hall of Fame player]] [[Joe Dumars]], who later served as team president.
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| *** The [[Milwaukee Bucks]], for [[Sidney Moncrief]].
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| *** The [[Brooklyn Nets#1967–1976: The ABA years|New York Nets]], for [[Wendell Ladner]], who died in [[Eastern Air Lines Flight 66|a 1975 plane crash]].
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| *** The [[Sacramento Kings]], for [[Chris Webber]].
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| *** The [[Utah Jazz]], for Hall of Fame player [[Adrian Dantley]].
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| ** In the [[National Hockey League|NHL]]:
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| *** The [[Boston Bruins]], for [[Hockey Hall of Fame|Hall of Famer]] [[Bobby Orr]].
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| *** The [[Montreal Canadiens]], for Hall of Famer [[Jean Beliveau]].
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| *** The [[New Jersey Devils]], for Hall of Famer [[Scott Stevens]].
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| *** The [[Philadelphia Flyers]], for [[Barry Ashbee]].
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| *** The [[Toronto Maple Leafs]] have a policy of not retiring numbers unless the player honoured either died or suffered a career-ending incident while a member of the team. Other players whose numbers would otherwise be retired instead have their numbers enshrined by the team as "Honoured Numbers", which remain in circulation for future players. The number 4 is currently honoured for Hall of Famer [[Red Kelly]].
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| ** In the [[National Football League|NFL]]:
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| *** The [[New York Giants]], for [[Pro Football Hall of Fame|Hall of Famer]] [[Tuffy Leemans]].
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| ==In other fields==
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| [[File:ICS Four.svg|right|thumb|100px|[[International maritime signal flag]] for 4]]
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| ''See also [[4 (disambiguation)]].''
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| * The phrase "[[four-letter word]]" is used to describe most [[profanity|swear]] words in the [[English language]], as most swear words do indeed possess four letters.
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| * Four (四, formal writing: 肆, [[pinyin]] sì) is considered an [[unlucky number]] in [[Chinese culture|Chinese]], [[Korean culture|Korean]], [[Culture of Vietnam|Vietnamese]] and [[Culture of Japan|Japanese]] cultures because it sounds like the word "death" (死, [[pinyin]] sǐ). Due to that, many numbered product lines skip the "four": e.g. [[Nokia]] [[cell phones]] (there is no series beginning with a 4), [[Microsoft Windows]] (which switched to "Windows 95" for version 4<ref>http://windowsteamblog.com/blogs/windowsvista/archive/2008/10/14/why-7.aspx</ref>{{Failed verification|date=December 2012}}), [[PalmOne, Inc.|Palm]] [[Personal digital assistant|PDAs]], the [[Leisure Suit Larry (series)|Leisure Suit Larry]] games, etc. Some buildings skip floor 4 or replace the number with the letter "F", particularly in heavily Asian areas. ''See [[tetraphobia]]'' and ''[[Numbers in Chinese culture]]''.
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| * The number of characters in a canonical [[four-character idiom]].
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| * In the [[ICAO spelling alphabet|NATO phonetic alphabet]], the digit 4 is called "fower".
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| * In [[Astrology]], [[Cancer (constellation)|Cancer]] is the 4th [[astrological sign]] of the [[Zodiac]].
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| * In [[Tarot]], [[The Emperor (Tarot card)|The Emperor]] is the fourth [[trump]] or [[Major Arcana]] card.
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| * In [[Nintendo]]'s ''[[Mario Kart]]'' series, four is the number of courses that each cup holds and there are four cups in the series: Mushroom Cup, Flower Cup, Star Cup and Special Cup
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| * In ''[[Tetris]]'', a game named for the Greek word for 4, every shape in the game is formed of 4 blocks each.
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| * 4 represents the number of Justices on the [[Supreme Court of the United States]] necessary to grant a writ of [[certiorari]] (i.e., agree to hear a case; it is one less than the number necessary to render a majority decision).
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| ==In music==
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| * In [[classical music]], [[Time signature|common time]] is constructed of four beats.
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| * The number of movements in a [[symphony]].
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| * The number of completed, numbered symphonies by [[Johannes Brahms]].
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| * The number of strings on a [[violin]], a [[viola]], a [[cello]], [[double bass]], a [[cuatro (instrument)|cuatro]] and a [[ukulele]], and the number of string pairs on a [[mandolin]].
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| * "Four colly birds" is the gift on the fourth day of Christmas in the carol "[[The Twelve Days of Christmas (song)|The Twelve Days of Christmas]]
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| * [[Four (Bloc Party album)|Four]], british rock album [[Bloc Party]]'s fourth full-length album.
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| ==Groups of four==
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| * Four rules: [[addition]], [[subtraction]], [[multiplication]], [[division (mathematics)|division]].
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| * [[Classical element#Classical elements in Greece|Greek classical elements]] ([[fire]], [[air]], [[water]], [[earth]]).
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| * [[Season|Four seasons]]: [[spring (season)|spring]], [[summer]], [[autumn]], [[winter]].
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| * Four [[Terrestrial planet|rocky planets]] in Earth's [[Solar System]]: [[Mercury (planet)|Mercury]], [[Venus]], [[Earth]], [[Mars]].
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| * Four is the minimal number of contemporary [[continent]]s: [[Americas]], [[Afro-Eurasia|Eurafrasia]], [[Australia (continent)|Sahul]], [[Antarctica]].
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| * Approximately four weeks (4 times 7 days) to a lunar month ([[synodic month]] = 29.53 days). Thus the number four is universally an integral part of primitive sacred calendars.
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| * Four [[cardinal directions]]: [[north]], [[south]], [[east]], [[west]].
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| * [[Four Temperaments]]: [[sanguine]], [[choleric]], [[melancholic]], [[phlegmatic]].
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| * [[Humorism|Four Humors]]: [[blood]], [[yellow bile]], [[black bile]], [[phlegm]].
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| * [[Four Great Ancient Capitals of China]]
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| * [[Four corner method]]
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| * [[Four cardinal principles|Cardinal principles]]
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| * [[Four cardinal virtues]]: justice, prudence, temperance, fortitude.
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| * Four canonical [[Christianity|Christian]] [[Gospels]], attributed to the [[Four Evangelists]] ([[Matthew the Evangelist|Matthew]], [[Mark the Evangelist|Mark]], [[Luke the Evangelist|Luke]], and [[John the Evangelist|John]])
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| * [[Four horsemen of the Apocalypse]]: [[war]], [[famine]], [[infectious disease|pestilence]], [[death]].
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| * Four [[suit (cards)|suits]] of [[playing card]]s: hearts, diamonds, clubs, spades.
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| * Four [[nation]]s of the [[United Kingdom]]: England, [[Wales]], [[Scotland]], [[Northern Ireland]].
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| * [[Four Noble Truths]] in the [[Buddhist]] religion.
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| * Four estates: [[politics]], [[public administration|administration]], [[judiciary]], [[journalism]]. Especially in the expression "[[Fourth Estate]]", which means journalism.
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| * [[Four Corners Monument|Four Corners]] is the only location in the United States where four [[U.S. state|states]] come together at a single point: [[Colorado]], [[Utah]], [[New Mexico]], and [[Arizona]].
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| * The [[Fantastic Four]]: Mr. Fantastic, The Invisible Woman, The Human Torch, The Thing.
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| * [[The Beatles]] were also known as the "Fab Four": John Lennon, Ringo Starr, George Harrison, Paul McCartney.
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| * [[Gang of Four (band)|Gang of Four]] is a British [[post-punk]] [[rock and roll|rock]] band formed in the late 1970s.
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| * Typically there are four string players in a classical [[string quartet]], usually two [[violin]]ists, a [[viola|violist]], and a [[cello|cellist]].
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| * Four rivers in the [[Garden of Eden]] ([[Book of Genesis|Genesis]] 2:10–14): [[Pishon]] (perhaps the Jaxartes or [[Syr Darya]]), [[Gihon]] (perhaps the Oxus or [[Amu Darya]]), Hiddekel ([[Tigris]]), and P'rat ([[Euphrates]])
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| * There are also four years in a single [[Olympiad]] (duration between the [[Olympic Games]]). Many major international sports competitions follow this cycle, among them the [[FIFA World Cup]] and its [[FIFA Women's World Cup|women's version]], the FIBA World Championships for [[FIBA World Championship|men]] and [[FIBA World Championship for Women|women]], and the [[Rugby World Cup]].
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| * Four opposed camps of the morality and nature of evil: [[moral absolutism]], [[amoralism]], [[moral relativism]], and [[moral universalism]].
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| * There are four limbs on the [[human]] body.
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| ==References==
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| {{Reflist}}
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| * Wells, D. ''[[The Penguin Dictionary of Curious and Interesting Numbers]]'' London: Penguin Group. (1987): 55 - 58
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| ==External links==
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| {{wiktionary|four}}
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| {{Commons category|4 (number)}}
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| * [http://www.marijn.org/everything-is-4 Marijn.Org on Why is everything four?]
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| * [http://www.samuel-beckett.net/Penelope/four_symbolism.html A few thoughts on the number four], by Penelope Merritt at samuel-beckett.net
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| * [http://www.numdic.com/4 The Number 4]
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| * [http://www.positiveintegers.org/4 The Positive Integer 4]
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| * [http://primes.utm.edu/curios/page.php/4.html Prime curiosities: 4]
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| {{Integers|zero}}
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| {{Superstitions}}
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| [[Category:Integers|04]]
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| [[Category:Superstitions about numbers]]
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