Argument
From Philosophical Logic
A logical argument is a combination of propositions, of which some are called premises and others conclusions, such that by asuming the truth of the premises it is rational to asume the truth of the conclusion.
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[edit] Valid/ invalid
An argument is valid if and only if the conclusion necessarily follows from 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 necessity 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.
[edit] Sound/ unsound
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.
[edit] Deductive/ inductive
In a deductive argument the premises justify the claim made by the conclusion to its full extent and with necessity. In an inductive argument the premises merely support the conclusion's truth.
[edit] Limits of the argument
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 by common sense. Yet spontaneous human judgement is a difficult criterium for truth, as it can easily be fooled by treacherous rhetorics and its own misjudgements.
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.
