How to Evaluate Arguments

When evaluating arguments, we have two main questions to ask:

1. Do the premises provide enough logical support for the conclusion?
2. Are the premises true?

In this article, we’ll discuss how to answer the first question. As we mentioned, the answer to this question depends on whether the argument is deductive or non-deductive.

Deductive and Non-Deductive Arguments

Validity applies to deductive arguments, strength applies to non-deductive arguments.

Let’s start with deductive arguments and validity.

• Definition: A valid argument is a deductive argument that succeeds in providing decisive logical support.

A valid argument is thus a deductive argument – an argument that attempts to establish conclusive support for its conclusion – that succeeds.

• Definition: An invalid argument is a deductive argument that fails in providing conclusive support.

For deductive arguments, you answer “yes” to the question “Do the premises provide enough logical support for the conclusion?” if the argument is valid, and you answer “no” if otherwise.

Take the following deductive argument:

Patrick’s jeans are blue, therefore, Patrick’s jeans are coloured.

If you throw a dice, either it lands on six or it doesn’t. So the dice has a 50% chance of landing on six.

If there is a purple elephant in the hall, then I am a giant turkey. There is a purple elephant in the hall. Therefore, I’m a giant turkey.

• Definition: A strong argument is a non-deductive argument that succeeds in providing probable, but not conclusive, logical support for its conclusion. A weak argument is a non-deductive argument that fails to provide probable support for its conclusion.

97% of vegetarians are healthy. Madison is a vegetarian. Therefore, Madison is probably healthy.

Bailey’s father is a plumber, so Bailey’s father has a van.

I think this one is also strong. Here’s my reasoning. Being a plumber is the kind of job that requires you to go around with tools and tools that are messy and get dirty and everything, and you don’t want to put it in a nice little car; you need space. In my experience, plumbers typically have vans. So then it would be quite reasonable to expect Bailey’s father to have a van if he’s a plumber.