Logic

Propositions are the material of our reasoning. It asserts that something is (or is not) the case. Any proposition may be affirmed or denied.

As logicians use the word an argument is any group of propositions of which one is claimed to follow from the others, which are regarded as providing support or grounds for the truth of that one. For an argument to be present there must be some structure within the cluster of propositions, a structure that captures or exhibits some inference. This structure we describe using the terms premise and conclusion.

The conclusion of an argument is the proposition that is affirmed on the basis of the other propositions of the argument. Those other propositions, which are affirmed (or assumed) as providing support for the conclusion, are the premises of the argument.

The simplest kind of argument consists of one premise and a conclusion. Each may be stated in separate sentences:

No one was present when life first appeared on earth. Therefore any statement about life’s origins should be considered as theory, not fact.

Or both the premise and the conclusion can be stated in one sentence:

 Since it turns out that all humans are descended from a small member of African ancestors in our recent evolutionary past, believing in profound differences between the races is as ridiculous as believing in a flat earth.

The statements of the argument’s conclusion may precede its statement of its single premise.