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(Expressions may be Arguments ; i.e., a Conjunction of expressions, each Conjunct of which is a Premise with the last being the Conclusion .)

"The pattern of reasoning that the truth table tabulates was '' uses them to place Truth Function s in a series. The wide influence of this work led to the spread of the use of truth tables.

Truth tables are used to compute the values of propositional expressions in an effective manner that is sometimes referred to as a '' Decision Procedure ''.
A propositional expression is either an Atomic Formula — a propositional constant, propositional variable, or propositional function term (for example, ''Px'') — or built up from atomic formulas by means of logical operators, for example, AND (\land), OR (\lor), NOT (\lnot). For instance, Fx \land Gx is a propositional expression.

The column headings on a truth table show (i) the propositional functions and/or variables, and (ii) the truth-functional expression built up from those propositional functions or variables and operators.
The rows show each possible valuation of T or '''F''' assignments to (i) and (ii).
In other words, each row is a distinct interpretation of (i) and (ii).

Truth tables for classical (i.e., bivalent) logic are limited to Boolean Logic systems where only two Truth Value s are possible, ''true'' or ''false'', usually denoted simply T and '''F''' in the tables (as remarked above).


LOGICAL CONJUNCTION

For example, take two propositional variables, A and B, and the logical operator " AND " (∧), signifying the conjunction "A and B" or AB.
In common English, if both A and B are true, then the conjunction "AB" is true; under all other possible assignments of truth values to AB, the conjunction is false.
This relationship is defined as follows:


LOGICAL DISJUNCTION

The OR (∨) relationship is defined as follows:


NEGATION

In a boolean logic system, all the operators can be explicitly defined this way.
For example, the NOT (¬) relationship is defined as follows:


LOGICAL NAND

Compound expressions can be constructed, using parenthesis to denote precedence.


The negation of conjunction ¬ (AB) ≡ A B, and the disjunction of negations ¬ A ∨ ¬ B are depicted as follows:


LOGICAL NOR

Truth tables can be used to prove Logical Equivalence .


The negation of disjunction ¬ (AB) ≡ A B, and the conjunction of negations ¬ A ∧ ¬ B are depicted as follows:

Comparing the above two truth tables, since the enumeration of all possible truth-values for A and B yields the same truth-value under both A B and ¬ A ∨ ¬ B; and both A B and ¬ A ∧ ¬ B, the two and two are logically equivalent correspondingly, and may be substituted for each other.
This equivalence is one of DeMorgan's Law s.


TRUTH TABLE FOR MOST COMMONLY USED LOGICAL OPERATORS

  • -5.---" class="copylinks">The 16 Possible Truth Functions Of 2 Binary Variables (P,Q Are Thus Boolean Variables) :



Key:
:T = true, F = false
:∧ = AND (logical conjunction)
:∨ = OR (logical disjunction)
: = XOR (exclusive or)
: = XNOR (exclusive nor)
:→ = Conditional "if-then"
:← = Conditional "(then)-if"

<↔>: (exclusive nor).

Johnston Diagram s, similar to Venn Diagram s and Euler Diagrams , provide a way of visualizing truth tables. An interactive Johnston Diagram illustrating truth tables is at LogicTutorial.com


CONDENSED TRUTH TABLES FOR BINARY OPERATORS

For binary operators, a condensed form of truth table is also used, where the row headings and the column headings specify the operands and the table cells specify the result. For example Boolean Logic uses this condensed truth table notation:

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