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The result is that the truth of either one of the connected statements requires the truth of the other (i.e. either both statements are true, or both are false), though it is controversial whether the connective thus defined is properly rendered by the English "if and only if"—with its pre-existing meaning.
For instance, two statements or more are logically incompatible if, and only if their conjunction is logically false. One statement logically implies another when it is logically incompatible with the negation of the other. A statement is logically true if, and only if its opposite is logically false. The opposite statements must contradict one ...
In specifying precisely which of the infinite number of truth-conditions for a sentence will count towards its meaning, one must take the meaning of the sentence as a guide. However, we wanted to specify meaning with truth-conditions, whereas now we are specifying truth-conditions with meaning, rendering the entire process fruitless.
(5) "∀x(Fx)" is true if, and only if, for all objects x, "Fx" is true. (6) "∃ x ( Fx )" is true if, and only if, there is an object x for which "Fx" is true. These explain how the truth conditions of complex sentences (built up from connectives and quantifiers ) can be reduced to the truth conditions of their constituents .
A class of connectives is truth-functional if each of its members is. For example, the connective "and" is truth-functional since a sentence like "Apples are fruits and carrots are vegetables" is true if, and only if, each of its sub-sentences "apples are fruits" and "carrots are vegetables" is true, and it is false otherwise. Some connectives ...
The meaning of a sentence is conveyed if the truth conditions for the sentence are understood. Additionally, there are many sentences that are understood although their truth condition is uncertain. One popular argument for this view is that some sentences are necessarily true—that is, they are true whatever happens to obtain. All such ...
Venn diagram of (true part in red) In logic and mathematics, the logical biconditional, also known as material biconditional or equivalence or biimplication or bientailment, is the logical connective used to conjoin two statements and to form the statement "if and only if" (often abbreviated as "iff " [1]), where is known as the antecedent, and the consequent.
a meaningful declarative sentence that is true or false, [citation needed] or; a proposition. Which is the assertion that is made by (i.e., the meaning of) a true or false declarative sentence. [1] [2] In the latter case, a (declarative) sentence is just one way of expressing an underlying statement.