http://www.unco.edu/philosophy/arg.html

An argument is a good argument in the strict sense of the term just in case it is either (a) a strong inductive argument with true premises or (b) a sound argument the conclusion of which isn’t included among the premises and the validity of which isn’t merely a function of its conclusion’s being a statement that couldn’t conceivably be false. (Note 1: the point of the first qualification in (b) is that circular pieces of reasoning shouldn’t qualify as good arguments (even though they are valid), and the point of the second is that we’re equally far from having a good argument in any such ridiculous “proof” of a mathematical or logical truth as, say, “Grass is green, hence 2 + 2 = 4” or “Whales aren’t fish, so Plato was a philosopher unless he wasn’t.” Note 2: valid arguments and strong inductive arguments are sometimes called “good arguments” even though they have false premises simply to indicate that the inferences they embody can’t be faulted on logical grounds alone. Maybe we should say that such arguments are good arguments in a loose sense of the term. Nothing can be faulted about the reasoning in such arguments.)