How to Identify and Evaluate an Argument
Identifying and evaluating arguments is a skill. It takes a lot of practice. Here are some techniques that may help.
- Identify the claim or thesis that the person is trying to convince you is true (this is the conclusion of the argument). (Conclusions are often, but not always, signaled by such words as "therefore." "so," or "thus.") Write it down.
- Identify the reasons that the person offers in support of
his or her claim (these are the premises for the argument). (Premises
are often, but not always, signaled by such words as "because," "for the
following reason," or "since"). Ask the question, "Why do you believe that?"
about the conclusion. The answer to this question should be the reasons
why the person thinks that the conclusion is true.
Note: Reasons are not the same thing as "causes." We are not interested in what caused someone to have a certain belief (e.g., because they were hit on the head as a child, or they were raised in a particular culture at a particular time). We are interested in the reasons that the person gives in support of his or her beliefs.
- List the premises in what seems to be the most logical
order with the conclusion at the bottom. (This will not necessarily
be the same order as the original.)
It should look like so:
And so on...
- Define the key terms. Ask the question, "What do you mean by...?" about key terms. Be sure that you are clear on what all the key terms mean (in particular, what the person means by them). If the person does not give an explicit definition, try to look at how she or he uses the term and make your best guess.
- Evaluate the argument.
- Look at the argument. Does the conclusion follow from the premises? (Here is one way to check: For the sake of argument, assume that the premises are true. Ask yourself, "Can I think of a case where the premises are true and the conclusion false?" If so, the argument is not deductively valid.)
- If the argument is not deductively valid, try to identify the gap in
the argument. Double check that you have given a fair representation of
Note: You will have to go back and forth between your own understanding of the argument and what the person says. In short, you need to check whether the flaws you find in the argument are because the person's reasoning is flawed, or because your understanding of it is flawed.
- If the argument is invalid, then you don't need to figure out if the premises are true. Even if they were true, they would not provide any support for the conclusion. So, their truth or falsity is not relevant. If the argument is valid, go to step (b). Note: Most arguments offered by philosophers are deductive arguments. They are intended to show that the conclusion necessarily follows from the premises. In other words, the conclusion of a valid argument with true premises will always, without exception, be true. Not all arguments are deductive, however. Some arguments are inductive. The claims of scientists, for instance, are generally supported by inductive arguments. Inductive arguments are intended to show that the conclusion follows from the premises with a very high probability. So, it is possible (though highly unlikely) for the conclusion of a good inductive argument to be false even when it has true premises.
- Test the truth of the premises. What reasons are there to think that
they are true? What reasons are there to think that they are false? What
further questions would need to be answered in order to determine whether
they are true or false?
- Often premises will contain "universal generalization" statements. "All men are mortal." "Those who believe in divinities believe in Gods." Ask the question, "Is that always true?" If you can find a case where it is not (this is a "counter-example"), then the universal generalization is false. You might want to check the text again to see if you got the correct universal generalization.
- If the premise seems obviously false, check back that you have not misrepresented the person's meaning.
a. Check whether the argument is deductively valid.
Note: Philosophers mean something very precise by "validity." By "valid" they don't mean "correct" or "acceptable." A "valid" argument is an argument where the conclusion follows logically from the premises--if you accept the premises, you are logically compelled to accept the conclusion. But valid arguments can be incorrect. That is, they can have false premises. All that validity means is that IF the premises are true, THEN the conclusion is true. If just one of the premises is false, all bets are off. Correct arguments are not just valid, but SOUND; that is, they are logically valid AND all their premises are true. In this course we will use "valid" to mean ONLY that the conclusion follows from the premises. We will use "sound" to mean that the argument is correct (valid + true premises).
b. Check whether the premises are true.
6. If the argument is deductively valid and the premises are true, then it is a good (sound) argument and you are rationally required to accept the conclusion. Why? Because the conclusion of a valid argument with true premises is always true. In other words, if you are presented with an argument for a conclusion you think is false, you will have to show that either (1) it is not logically valid--the conclusion does not follow from the premises, or (2) that at least one of the premises is false.
Assignment: Follow the above steps and identify and evaluate the following argument. Bring your results to class. This one gets under some people's skin. Remember, your job is to dispassionately identify and evaluate the soundness of the argument.
"If God does not exist, then life is futile. If the God of the Bible does exist, then life is meaningful. Only the second of these two alternatives allows us to live happily and consistently. Therefore, a rational person ought to choose Biblical Christianity" (William Lane Craig "The Absurdity of Life Without God," p. 53-54).