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Venn diagram of (true part in red) In logic and mathematics, the logical biconditional, also known as material biconditional or equivalence or bidirectional implication 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.
[1] Being a valid argument does not necessarily mean the conclusion will be true. It is valid because if the premises are true, then the conclusion has to be true. This can be proven for any valid argument form using a truth table which shows that there is no situation in which there are all true premises and a false conclusion. [2]
conclusion iff conditions. it uses sentences of the form: conclusion if conditions. to reason forwards from conditions to conclusions or backwards from conclusions to conditions. The database semantics is analogous to the legal principle expressio unius est exclusio alterius (the express mention of one thing excludes all others). Moreover, it ...
Quine devotes the first chapter of Philosophy of Logic to this issue. [2] Historians have not even been able to agree on what Aristotle took as constituents. [3] Argument–deduction–proof distinctions are inseparable from what have been called the consequence–deducibility distinction and the truth-and-consequence conception of proof. [1]
Notice some of the terms repeat: men is a variation man in premises one and two, Socrates and the term mortal repeats in the conclusion. The argument would be just as valid if both premises and conclusion were false. The following argument is of the same logical form but with false premises and a false conclusion, and it is equally valid:
He shows how the chance observations of a few results of the form 4 = 2 + 2, 6 = 3 + 3, 8 = 3 + 5, 10 = 3 + 7, etc., may prompt a sharp mind to formulate the conjecture that every even number greater than 4 can be represented as the sum of two odd prime numbers. This is the well known Goldbach's conjecture. The first problem in the first ...
But this is a misconception that does not reflect how valid deduction is defined in the field of logic: a deduction is valid if it is impossible for its premises to be true while its conclusion is false, independent of whether the premises or the conclusion are particular or general. [2] [9] [1] [5] [3] Because of this, some deductive ...
The Polish logician Alfred Tarski identified three features of an adequate characterization of entailment: (1) The logical consequence relation relies on the logical form of the sentences: (2) The relation is a priori, i.e., it can be determined with or without regard to empirical evidence (sense experience); and (3) The logical consequence ...