Negation

In logic, negation, also called the logical not or logical complement, is an operation that takes a proposition P to another proposition "not P", written ¬P, ∼P, P′[1] or P‾[2]. It is interpreted intuitively as being true when P is false, and false when P is true.[3][4] For example, if P is "The dog runs", then "not P" is "The dog does not run". An operand of a negation is called a negand or negatum.[5]

Negation is a unary logical connective. It may furthermore be applied not only to propositions, but also to notions, truth values, or semantic values more generally. In classical logic, negation is normally identified with the truth function that takes truth to falsity (and vice versa). In intuitionistic logic, according to the Brouwer–Heyting–Kolmogorov interpretation, the negation of a proposition P is the proposition whose proofs are the refutations of P.

## Contents

* 1 Definition
* 2 Notation
* 2.1 Precedence
* 3 Properties
* 3.1 Double negation
* 3.2 Distributivity
* 3.3 Linearity
* 3.4 Self dual
* 3.5 Negations of quantifiers
* 4 Rules of inference
* 5 Programming language and ordinary language
* 5.1 Usage in colloquial language
* 6 Kripke semantics
* 7 See also
* 8 References
* 9 Further reading
* 10 External links

## Definition

Classical negation is an operation on one logical value, typically the value of a proposition, that produces a value of true when its operand is false, and a value of false when its operand is true. Thus if statement P is true, then ¬P (pronounced "not P") would then be false; and conversely, if ¬P is true, then P would be false.

The truth table of ¬P is as follows:

P | ¬P

|

True | False
False | True

Negation can be defined in terms of other logical operations. For example, ¬P can be defined as P->⊥ (where -> is logical consequence and ⊥ is absolute falsehood). Conversely, one can define ⊥ as Q∧¬Q for any proposition Q (where ∧ is logical conjunction). The idea here is that any contradiction is false, and while these ideas work in both classical and intuitionistic logic, they do not work in paraconsistent logic, where contradictions are not necessarily false. As a further example, negation can be defined in terms of NAND and can also be defined in terms of NOR.

Algebraically, classical negation corresponds to complementation in a Boolean algebra, and intuitionistic negation to pseudocomplementation in a Heyting algebra. These algebras provide a semantics for classical and intuitionistic logic.

## Notation

The negation of a proposition p is notated in different ways, in various contexts of discussion and fields of application. The following table documents some of these variants:

Notation  | Plain text  | Vocalization

|
|

¬p | ¬p , 7p[6] | Not p
∼p | ~p | Not p
−p | -p | Not p
Np |  | En p
p′ | p' |

* p prime,
* p complement

p‾ |  ̅p |

* p bar,
* Bar p

!p | !p |

* Bang p
* Not p

The notation Np is Polish notation.

In set theory, ∖ is also used to indicate 'not in the set of': U∖A is the set of all members of U that are not members of A.

Regardless how it is notated or symbolized, the negation ¬P can be read as "it is not the case that P", "not that P", or usually more simply as "not P".

### Precedence

As a way of reducing the number of necessary parentheses, one may introduce precedence rules: ¬ has higher precedence than ∧, ∧ higher than ∨, and ∨ higher than →. So for example, P∨Q∧¬R->S is short for (P∨(Q∧(¬R)))->S.

Here is a table that shows a commonly used precedence of logical operators.[7]

Operator | Precedence

|

¬ | 1
∧ | 2
∨ | 3
-> | 4
↔ | 5

## Properties

### Double negation

Within a system of classical logic, double negation, that is, the negation of the negation of a proposition P, is logically equivalent to P. Expressed in symbolic terms, ¬¬P≡P. In intuitionistic logic, a proposition implies its double negation, but not conversely. This marks one important difference between classical and intuitionistic negation. Algebraically, classical negation is called an involution of period two.

However, in intuitionistic logic, the weaker equivalence ¬¬¬P≡¬P does hold. This is because in intuitionistic logic, ¬P is just a shorthand for P->⊥, and we also have P->¬¬P. Composing that last implication with triple negation ¬¬P->⊥ implies that P->⊥ .

As a result, in the propositional case, a sentence is classically provable if its double negation is intuitionistically provable. This result is known as Glivenko's theorem.

### Distributivity

De Morgan's laws provide a way of distributing negation over disjunction and conjunction:

¬(P∨Q)≡(¬P∧¬Q), and
¬(P∧Q)≡(¬P∨¬Q).

### Linearity

Let ⊕ denote the logical xor operation. In Boolean algebra, a linear function is one such that:

If there exists a0,a1,…,an∈{0,1}, f(b1,b2,…,bn)=a0⊕(a1∧b1)⊕…⊕(an∧bn), for all b1,b2,…,bn∈{0,1}.

Another way to express this is that each variable always makes a difference in the truth-value of the operation, or it never makes a difference. Negation is a linear logical operator.

### Self dual

In Boolean algebra, a self dual function is a function such that:

f(a1,…,an)=¬f(¬a1,…,¬an) for all a1,…,an∈{0,1}. Negation is a self dual logical operator.

### Negations of quantifiers

In first-order logic, there are two quantifiers, one is the universal quantifier ∀ (means "for all") and the other is the existential quantifier ∃ (means "there exists"). The negation of one quantifier is the other quantifier (¬∀xP(x)≡∃x¬P(x) and ¬∃xP(x)≡∀x¬P(x)). For example, with the predicate P as "x is mortal" and the domain of x as the collection of all humans, ∀xP(x) means "a person x in all humans is mortal" or "all humans are mortal". The negation of it is ¬∀xP(x)≡∃x¬P(x), meaning "there exists a person x in all humans who is not mortal", or "there exists someone who lives forever".

## Rules of inference

See also: Double negation

There are a number of equivalent ways to formulate rules for negation. One usual way to formulate classical negation in a natural deduction setting is to take as primitive rules of inference negation introduction (from a derivation of P to both Q and ¬Q, infer ¬P; this rule also being called reductio ad absurdum), negation elimination (from P and ¬P infer Q; this rule also being called ex falso quodlibet), and double negation elimination (from ¬¬P infer P). One obtains the rules for intuitionistic negation the same way but by excluding double negation elimination.

Negation introduction states that if an absurdity can be drawn as conclusion from P then P must not be the case (i.e. P is false (classically) or refutable (intuitionistically) or etc.). Negation elimination states that anything follows from an absurdity. Sometimes negation elimination is formulated using a primitive absurdity sign ⊥. In this case the rule says that from P and ¬P follows an absurdity. Together with double negation elimination one may infer our originally formulated rule, namely that anything follows from an absurdity.

Typically the intuitionistic negation ¬P of P is defined as P->⊥. Then negation introduction and elimination are just special cases of implication introduction (conditional proof) and elimination (modus ponens). In this case one must also add as a primitive rule ex falso quodlibet.

## Programming language and ordinary language

As in mathematics, negation is used in computer science to construct logical statements.

if (!(r == t))

/*...statements executed when r does NOT equal t...*/

The exclamation mark "`!`" signifies logical NOT in B, C, and languages with a C-inspired syntax such as C++, Java, JavaScript, Perl, and PHP. "`NOT`" is the operator used in ALGOL 60, BASIC, and languages with an ALGOL- or BASIC-inspired syntax such as Pascal, Ada, and Eiffel. Some languages (C++, Perl, etc.) provide more than one operator for negation. A few languages like PL/I and Ratfor use `¬` for negation. Most modern languages allow the above statement to be shortened from `if (!(r == t))` to `if (r != t)`, which allows sometimes, when the compiler/interpreter is not able to optimize it, faster programs.

In computer science there is also bitwise negation. This takes the value given and switches all the binary 1s to 0s and 0s to 1s. This is often used to create ones' complement (or "`~`" in C or C++) and two's complement (just simplified to "`-`" or the negative sign, as this is equivalent to taking the arithmetic negation of the number).

To get the absolute (positive equivalent) value of a given integer the following would work as the "`-`" changes it from negative to positive (it is negative because "`x < 0`" yields true)

unsigned int abs(int x)

if (x < 0)
return -x;
else
return x;

To demonstrate logical negation:

unsigned int abs(int x)

if (!(x < 0))
return x;
else
return -x;

Inverting the condition and reversing the outcomes produces code that is logically equivalent to the original code, i.e. will have identical results for any input (depending on the compiler used, the actual instructions performed by the computer may differ).

In C (and some other languages descended from C), double negation (`!!x`) is used as an idiom to convert `x` to a canonical Boolean, ie. an integer with a value of either 0 or 1 and no other. Although any integer other than 0 is logically true in C and 1 is not special in this regard, it is sometimes important to ensure that a canonical value is used, for example for printing or if the number is subsequently used for arithmetic operations.[8]

### Usage in colloquial language

The convention of using `!` to signify negation occasionally surfaces in colloquial language, as computer-related slang for not. For example, the phrase `!clue` is used as a synonym for "no-clue" or "clueless".[9][10]

Another example is the expression `!vote` which means "not a vote".[11] In this context, the exclamation mark is used at Wikipedia to survey opinions while negating "majority rule", in order "to have a consensus-building discussion, where the proper course is determined by the strength of the respective arguments."[11]

## Kripke semantics

In Kripke semantics where the semantic values of formulae are sets of possible worlds, negation can be taken to mean set-theoretic complementation (see also possible world semantics for more).

## See also

* Affirmation and negation (grammatical polarity)
* Ampheck
* Apophasis
* Binary opposition
* Bitwise NOT
* Contraposition
* Cyclic negation
* Negation as failure
* NOT gate
* Plato's beard
* Square of opposition

## References

1. ↑ Virtually all Turkish high school math textbooks use p' for negation due to the books handed out by the Ministry of National Education representing it as p'.
2. ↑ "NEGATION definition and meaning | Collins English Dictionary" (in en). 2025-12-15. https://www.collinsdictionary.com/dictionary/english/negation.
3. ↑ Weisstein, Eric W.. "Negation" (in en). https://mathworld.wolfram.com/Negation.html.
4. ↑ "Logic and Mathematical Statements - Worked Examples". https://www.math.toronto.edu/preparing-for-calculus/3_logic/we_3_negation.html.
5. ↑ Beall, Jeffrey C. (2010) (in en). Logic: the basics (1. publ ed.). London: Routledge. pp. 57. ISBN 978-0-203-85155-5.
6. ↑ Used as makeshift in early typewriter publications, e.g. Richard E. Ladner (Jan 1975). "The circuit value problem is log space complete for P". ACM SIGACT News 7 (101): 18-20. doi:10.1145/990518.990519.
7. ↑ O'Donnell, John; Hall, Cordelia; Page, Rex (2007), Discrete Mathematics Using a Computer, Springer, p. 120, ISBN 9781846285981, https://books.google.com/books?id=KKxyQQWQam4C&pg=PA120 .
8. ↑ Egan, David. "Double Negation Operator Convert to Boolean in C". https://dev-notes.eu/2019/10/Double-Negation-Operator-Convert-to-Boolean-in-C/.
9. ↑ Raymond, Eric and Steele, Guy. The New Hacker's Dictionary, p. 18 (MIT Press 1996).
10. ↑ Munat, Judith. Lexical Creativity, Texts and Context, p. 148 (John Benjamins Publishing, 2007).
11. ↑ 11.0 11.1 Harrison, Stephen. "Wikipedia's War on the Daily Mail", Slate Magazine (July 1, 2021).

## Further reading

* Gabbay, Dov, and Wansing, Heinrich, eds., 1999. What is Negation?, Kluwer.
* Horn, L., 2001. A Natural History of Negation, University of Chicago Press.
* G. H. von Wright, 1953–59, "On the Logic of Negation", Commentationes Physico-Mathematicae 22.
* Wansing, Heinrich, 2001, "Negation", in Goble, Lou, ed., The Blackwell Guide to Philosophical Logic, Blackwell.
* Tettamanti, Marco; Manenti, Rosa; Della Rosa, Pasquale A.; Falini, Andrea; Perani, Daniela; Cappa, Stefano F.; Moro, Andrea (2008). "Negation in the brain: Modulating action representation". NeuroImage 43 (2): 358–367. doi:10.1016/j.neuroimage.2008.08.004. PMID 18771737.

## External links

* Horn, Laurence R.; Wansing, Heinrich. "Negation". in Zalta, Edward N.. Stanford Encyclopedia of Philosophy. https://plato.stanford.edu/entries/negation/.
* Hazewinkel, Michiel, ed. (2001), "Negation", Encyclopedia of Mathematics, Springer Science+Business Media B.V. / Kluwer Academic Publishers, ISBN 978-1-55608-010-4, https://www.encyclopediaofmath.org/index.php?title=p/n066170
* NOT, on MathWorld

Tables of Truth of composite clauses

* "Table of truth for a NOT clause applied to an END sentence". http://www.math.hawaii.edu/~ramsey/Logic/NotAnd.html.
* "NOT clause of an END sentence". http://www.math.hawaii.edu/~ramsey/Logic/NotAnd.html.
* "NOT clause of an OR sentence". http://www.math.hawaii.edu/~ramsey/Logic/NotOr.html.
* "NOT clause of an IF...THEN period". http://www.math.hawaii.edu/~ramsey/Logic/NotIfThen.html.

* v
* t
* e

Logical connectives

* Tautology/True ⊤

* Alternative denial (NAND gate) ↑
* Converse implication <-
* Implication (IMPLY gate) ->
* Disjunction (OR gate) ∨

* Negation (NOT gate) ¬
* Exclusive or (XOR gate) ↮
* Biconditional (XNOR gate) ↔
* Statement

* Joint denial (NOR gate) ↓
* Nonimplication (NIMPLY gate) ↛
* Converse nonimplication ↚
* Conjunction (AND gate) ∧

* Contradiction/False ⊥

* v
* t
* e

Common logical symbols

∧ or &

and

¬ or ~

not

implies

implies,
superset

iff

nand

universal
quantification

existential
quantification

tautology

false,
contradiction

entails,
proves

entails,
therefore

therefore

because

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* v
* t
* e

Mathematical logic

General|

* Formal language
* Formation rule
* Formal proof
* Formal semantics
* Well-formed formula
* Set
* Element
* Class
* Classical logic
* Axiom
* Rule of inference
* Relation
* Theorem
* Logical consequence
* Type theory
* Symbol
* Syntax
* Theory

Systems|

* Formal system
* Deductive system
* Axiomatic system
* Hilbert style systems
* Natural deduction
* Sequent calculus

Traditional logic|

* Proposition
* Inference
* Argument
* Validity
* Cogency
* Syllogism
* Square of opposition
* Venn diagram

Propositional calculus
and Boolean logic

* Boolean functions
* Propositional calculus
* Propositional formula
* Logical connectives
* Truth tables
* Many-valued logic

Predicate logic|

* First-order
* Quantifiers
* Predicate
* Second-order
* Monadic predicate calculus

Naive set theory|

* Set
* Empty set
* Element
* Enumeration
* Extensionality
* Finite set
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* Subset
* Power set
* Countable set
* Uncountable set
* Recursive set
* Domain
* Codomain
* Image
* Map
* Function
* Relation
* Ordered pair

Set theory|

* Foundations of mathematics
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* Axiom of choice
* General set theory
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* Von Neumann–Bernays–Gödel set theory
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Model theory|

* Model
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* Validity

Proof theory|

* Formal proof
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Computability
theory|

* Recursion
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* Computable function
* Primitive recursive function

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