Sound and Cogent Arguments

So far we have talked about the kind of support that can be given for conclusions: deductive and non-deductive.

We defined an argument as being valid if it’s a deductive argument for which the premises succeed in providing conclusive support for the conclusion.

And we defined an argument as being strong if it’s a non-deductive argument in which the premises succeed in providing strong support for the conclusion.

By that, we mean that, if the premises are true, then the conclusion would be given the appropriate support for also being true.

But we haven’t said anything yet about whether the premises are true or not. This is what we do when we evaluate whether arguments are sound or cogent.

Sound and Cogent Arguments

Validity and strength of arguments do not on their own tell us whether arguments are good or bad. We’ve actually seen rubbish arguments that were valid. That’s why we need to introduce two further concepts for arguments: being sound and being cogent.

Sound Arguments

• Definition: A sound argument is a valid argument that has true premises.

Firstly, a sound argument is a deductive argument. It’s trying to establish conclusive support for its conclusion. Secondly, the argument is valid: the premises, if true, would guarantee that the conclusion is also true. And on top of all that, the premises are actually true. Therefore, a sound argument guarantees that its conclusion is true.

We say that a sound argument is a good argument. It is a good argument because it guarantees that the conclusion is true. It would be irrational for you not to believe the conclusion of a sound argument.

Of course, sound arguments are very rare, because they’re very hard to establish. But, some arguments are sound.

Sound Argument Example

The province of Québec is part of Canada. Patrick was born in Québec. Therefore, Patrick was born in Canada.

Further Sound Argument Examples

I drank coffee this morning; therefore, I drank something this morning.

Patrick got married on January 4, 2014. Patrick has not been divorced and Patrick is not a widower. Therefore, Patrick is not a bachelor.

Cogent Arguments

• Definition: A cogent argument is a strong non-deductive argument that has true premises.

Cogent Argument Example

Patrick was born in North America and Patrick wasn’t born in Mexico. It’s thus quite probable that Patrick was born in the USA.

Another Cogent Argument Example

I had coffee this morning. Therefore, it’s quite likely that I drank something this morning.

This is a strong argument with true premises, so it is cogent and therefore, good. But the conclusion is not guaranteed. It may be that I had coffee this morning by eating it, or by some other means. But of course, this is very unlikely, so the argument is strong, though it’s still possible that the conclusion is false. Still, this is cogent and therefore, a good argument.