In logic, a series of
statements of which the last is said to be the
conclusion, and the others the premisses or evidence for the conclusion.
An argument is deductively (also: logically) valid
if and only if in no case where the
premisses are all true the conclusion is not true.
Or to put this positively: Iff in every case where the premisses are all
true, the conclusion is also true.
Note that arguments may be hypothetical, namely in all those cases where not
that are used in it are known to be true.