Deductive Inference and Its Logical Bases

Abstract

When on the basis of my being convinced that today is Saturday I arrive at the conviction that tomorrow is Sunday, then it means that from the fact of today being Saturday I have inferred that tomorrow is Sunday. Inference is the intellectual process whereby someone accepts a proposition or a set of propositions as true, and arrives on that basis at a conviction about the truth of another proposition. Those propositions on the basis of which we recognize the truth of other propositions; or—in other words—those propositions from which the inference is drawn, are called the premises of the inference. The proposition which is regarded as true as a result of the inference process is called the conclusion. In the example quoted above the premise was the proposition: Today is Saturday’, while the conclusion was the proposition: ‘Tomorrow is Sunday’. More precisely, in the inference there was still another premise, not explicit but assumptive, that the conditional sentence: ‘If today is Saturday, then tomorrow is Sunday’ is true. This premise has not been expressed, because everybody knows that if today is Saturday, then tomorrow is Sunday; so there is no need of repeating it. An assumptive premise of somebody’s inference is called an enthymematic premise (retained in mind, in Greek: en thymo).