Definitions

Argument:

any group of propositions of which one is claimed to follow logically from the others.

Inference:

the reasoning process by which a logical relation such as entailment is perceived.

Entailment:

a relation between or among propositions such that the truth of one proposition is determined by the truth of another proposition or propositions and such that this determination is a function solely of the meanings of the propositions concerned.

Valid Argument:

a deductive argument whose conclusion follows necessarily from its premiss or premisses. (Usually an inference is said to be valid if it is permitted by the laws of some logic.)

Sound Argument:

a valid deductive argument which has true premisses. (Obviously, the conclusion is true as well.)