In the last article I briefly described what a ‘philosophical argument’ means. This article continues on this, so far, short series and looks at how we can assess the quality of an argument and what it means to say that an argument is valid or sound. As often is the case, it starts with some detective work.

Our main clues are the premises. Simply put, premises serve as the basis of my final conclusion, of the point that I want to make – of my argument. For example:

my (conclusion/point) argument is = all people are animals

You could ask me – OK, what is the basis of your argument? Or in ‘human’ language – why (why do I claim that all people are animals)?

As an answer I turn to my premises (reasons that serve as basis of my argument):

I could answer – because all people are mammals and all mammals are animals.

To put it as a ‘formula’:

Premise 1: all mammals are animals

Premise 2: all people are mammals

Conclusion (argument): all people are animals

This is an example of a valid and sound argument. Why? Firstly, all of its premises are true and, secondly, the truth of the premises carries over to the conclusion (the conclusion can be inferred from the premises).

An argument can be valid and not sound or not valid and not sound but it can never be sound and not valid at the same time. This is because soundness of an argument must consist of both its validity (truth of the premises being able to carry over to the conclusion) and the truthfulness of its premises.

Here is the same argument but slightly amended to render it valid but not sound:

Premise 1: all animals are mammals

Premise 2: all people are mammals

Conclusion (argument): all people are animals

What’s wrong here? The argument is still valid because the conclusion follows from both premises. So, if both premises were true, this truth does indeed carry over to the conclusion. However, premise 1 is not true. Not all animals are mammals, there are also reptiles, insects and others. Because of this the argument is not sound.

Finally, here is the same example altered so that becomes both not valid and not sound:

Premise 1: all animals are mammals

Premise 2: some mammals and people share their natural habitat

Conclusion (argument): all people are animals

As already established, premise 1 is not true, so this immediately signals that the argument cannot be sound. But is it still valid? Can the conclusion be inferred from the premises? No, it cannot. Even if both premises were true, their ‘message’ doe snot carry over to the conclusion. Simply put, there is no (valid) link between the claim that all people are animals and the other two claims that are supposed to serve as support for this conclusion.

And that is how you can evaluate the quality of arguments! Not just in philosophy, by the way. You would be surprised 🙂

keep exploring!