2.3: Arguments

The common sense everyday way to assess a claim for truth or falsity is to consider the reasons for holding it or rejecting it. Sometimes good reasons take the form of simple observations. I have a good reason for thinking my bicycle has a flat tire when I see the tire sagging on the rim or hear air hissing out of the tube. But often the business of identifying and evaluating reasons is a bit more involved. Since philosophy proceeds by formulating and evaluating the reasons for and against holding various positions, we will want to take a closer look at just how this goes. We will do so in the remainder of this chapter with the informal introduction to logic and critical thinking.

An argument is a reason for taking something to be true. Arguments consist of two or more claims, one of which is a conclusion. The conclusion is the claim the argument purports to give a reason for believing. The other claims are the premises. The premises of an argument taken together are offered as a reason for believing its conclusion.

Some arguments provide better reasons for believing their conclusions than others. In case you have any doubt about that, consider the following examples:

1. Sam is a line cook.
2. Line cooks generally have good of kitchen skills.
3. So, Sam can probably cook well.

1. Sam is a line cook.
2. Line cooks generally aren’t paid very well.
3. So, Sam is probably a millionaire.

The premises in the first argument provide pretty good support for thinking Sam can cook well. That is, assuming the premises in the first argument are true, we have a good reason to think that its conclusion is true. The premises in the second argument give us no reason to think Sam is a millionaire. So whether or not the premises of an argument support its conclusion is a key issue. Now consider these examples:

1. Boston is in Massachusetts.
2. Massachusetts is east of the Rockies.
3. So Boston is east of the Rockies.

1. Boston is in California.
2. California is west of the Rockies.
3. So Boston is west of the Rockies.

Again, the first of these two arguments looks pretty good, the second not so much. But the problem with the second argument here is different. If its premises were true, then we would have a good reason to think the conclusion is true. That is, the premises do support the conclusion. But the first premise of the second argument just isn’t true. Boston is not in California. So the latter pair of arguments suggests another key issue for evaluating arguments. Good arguments have true premises.

That is pretty much it. A good argument is an argument that has true premises that, when taken together, support its conclusion. So, evaluating an argument involves just these two essential steps:

• Determine whether or not the premises are true.
• Determine whether or not the premises support the conclusion (that is, whether we have grounds to think the conclusion is true if all of the premises are true).

Determining whether an argument’s premises are true often involves evaluating further arguments in support of those premises. An argument might be the last link in a long chain of reasoning. In this case, the quality of the argument depends on the whole chain. And since arguments can have multiple premises, each of which might be supported by further arguments, evaluating one argument might be more involved yet, since its conclusion is really supported by a rich network of reasoning, not just one link and then another. While the potential for complication should be clear, the basic idea should be pretty familiar. Think of the regress of“why” questions many of us tormented our parents with as children. Even at a young age we understood that the reasons for believing one thing can depend on the reasons for believing a great many other things.

However involved the network of reasons supporting a given conclusion might be, it seems that there must be some starting points. That is, it seems there must be some reasons for believing things that don’t themselves need to be justified in terms of further reasons. Otherwise the network of supporting reasons would go on without end. The issue we are facing here is one of identifying the ultimate foundations of knowledge and justified belief. This is a big epistemological issue and we will return to it later in the course. For now, let’s consider one potential answer we are already familiar with. In the sciences our complex chains of reasoning seem to proceed from the evidence of the senses. We think that evidence provides the foundation for our edifice of scientific knowledge. Sounds great for science, but where does this leave philosophy? Does philosophy entirely lack evidence on which its reasoning can be based? Philosophy does have a kind of evidence to work from and that evidence is provided by philosophical problems. When we encounter a problem in philosophy this often tells us that the principles and assumptions that generate that problem can’t all be correct. This might seem like just a subtle clue that leaves us far from solving the big mysteries. But clues are evidence just the same. As we will discuss in our chapter on the philosophy of science, science doesn’t really have it much easier. Sensory evidence by itself doesn’t tell us as much about the nature of the world as we’d like to suppose. Scientific evidence provides clues, but there remains a good deal of problem solving to do in science as well as in philosophy.

So we can assess the truth or falsity of the premises of an argument by examining evidence or by evaluating further argument in support of the premises. Now we will turn to the other step in evaluating arguments and consider the ways in which premises can support or fail to support their conclusions. The question of support is distinct from the question of whether the premises are true. When we ask whether the premises support the conclusions we are asking whether we’d have grounds for accepting the conclusion assuming the premises are true. In answering this question we will want to apply one of two standards of support: deductive validity or inductive strength.