Corresponding conditional

In logic, the corresponding conditional of an argument (or derivation) is a material conditional whose antecedent is the conjunction of the argument's (or derivation's) premises and whose consequent is the argument's conclusion. An argument is valid if and only if its corresponding conditional is a logical truth. It follows that an argument is valid if and only if the negation of its corresponding conditional is a contradiction. Therefore, the construction of a corresponding conditional provides a useful technique for determining the validity of an argument. Consider the argument A: Either it is hot or it is cold It is not hot Therefore it is cold This argument is of the form: Either P or Q Not P Therefore Q or (using standard symbols of propositional calculus): P Q P

Q The corresponding conditional C is: IF ((P or Q) and not P) THEN Q or (using standard symbols): ((P Q) P) Q and the argument A is valid just in case the corresponding conditional C is a logical truth. If C is a logical truth then C entails Falsity (The False). Thus, any argument is valid if and only if the denial of its corresponding conditional leads to a contradiction. If we construct a truth table for C we will find that it comes out T (true) on every row (and of course if we construct a truth table for the negation of C it will come out F (false) in every row. These results confirm the validity of the argument A Some arguments need first-order predicate logic to reveal their forms and they cannot be tested properly by truth tables forms. Consider the argument A1: Some mortals are not Greeks Some Greeks are not men Not every man is a logician Therefore Some mortals are not logicians To test this argument for validity, construct the corresponding conditional C1 (you will need first-order predicate logic), negate it, and see if you can derive a contradiction from it. If you succeed, then the argument is valid. Instead of attempting to derive the conclusion from the premises proceed as follows.

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Related concepts (2)

Validity (logic)

In logic, specifically in deductive reasoning, an argument is valid if and only if it takes a form that makes it impossible for the premises to be true and the conclusion nevertheless to be false. It is not required for a valid argument to have premises that are actually true, but to have premises that, if they were true, would guarantee the truth of the argument's conclusion. Valid arguments must be clearly expressed by means of sentences called well-formed formulas (also called wffs or simply formulas).

Logic

Logic is the study of correct reasoning. It includes both formal and informal logic. Formal logic is the science of deductively valid inferences or logical truths. It studies how conclusions follow from premises due to the structure of arguments alone, independent of their topic and content. Informal logic is associated with informal fallacies, critical thinking, and argumentation theory. It examines arguments expressed in natural language while formal logic uses formal language.