A logical argument is a combination of propositions, of which some are called premises and others conclusions, such that by assuming the truth of the premises it is rational to assume the truth of the conclusion.

Valid/ invalidEdit

The validity of an argument depends on whether it is deductive or inductive. However, in general terms, an argument is valid if the truth of the conclusion follows from the truth of the premises. Thus, given that all premises are true, the conclusion is true and it is impossible to exist in any other way. A valid argument can give false conclusions should any premise be false. Arguments of this sort can be good or bad depending on the truth of the premises.

All arguments that are not valid are invalid. That is, if any conclusion is not a logical consequence of the premises, then the argument is invalid. The premises only support the conclusion. An invalid argument is good or bad depending on how well the premises support the conclusion.

Sound/ unsoundEdit

A sound argument is an argument, where all the premises are true and the reasoning is valid. If either is missing the argument is called unsound.

Deductive/ inductiveEdit

In a deductive argument the premises justify the claim made by the conclusion to its full extent and with necessity. In other words, the conclusion's truth is derived from the truth of the premises. In an inductive argument the premises merely support the conclusion's truth. The truth of the conclusion is not necessary, but probable given the truth of the premises.

Limits of the argumentEdit

It is a subject of logic to examine the nature of the connection between the premises and the conclusion. At first guess one would assume, that the conclusion's truth, based on the truth of the premises and the logic of the argument should be somehow understood intuitively or be compelling to common sense. Yet human intuition is a difficult criterion for truth, as it can easily be fooled.

Therefore other criteria have to be found for testing the validity of an argument. Finding and examing these criteria is among philosophical logic's major aims.