Fallacies and Forms

There are a variety of reasons why an argument may fail to be a good one. The most obvious way in which an argument can fail is, of course, by having premises that are not all true. But, as we have indicated, the assessment of the truth or falsity of the premises of an argument is not typically one of our primary concerns. What does concern us is those cases where an argument is one in which it is purported that the premises give a certain kind of support to the conclusion, but do not in fact give such support. We shall speak of such arguments as fallacious. We will not, save in certain special cases, speak of an argument as fallacious simply because it has false premises. It is typically better, in such a case, to point out the false premises rather than attempting to apply some label. Again, we will typically speak of an argument as fallacious when the premises of the argument do not give support to the conclusion, or do not give the kind of support that they purport to give.

If we reconsider our account of would-be deductive arguments we can see that any invalid argument is a fallacious arguments. The argument is one in which the premises purport to give conclusive support to the conclusion. But, since it is invalid, the premises do not give such support to the conclusion. Consequently we can classify invalid arguments as fallacious. But typically it is more perspicuous- clearer- simply to note that they are invalid. In the case of inductive arguments, any argument in which the premises give no support to the conclusion, or such weak support as to be of no significance is a fallacious argument.

Certain ways of arguing poorly, certain fallacious arguments, are so common that we shall identify them and give them labels. In this case we speak of them as committing a fallacy. (We could speak of any fallacious argument as committing a fallacy, but since we will not give labels to each and every mistake one could conceivably make, we will typically speak of

an argument as committing a fallacy if we have a label, and simply as fallacious otherwise. The labels we will use are introduced at various later points in the text.)

It is important to bear in mind that the comment that an argument is fallacious is not typically a comment about the truth or falsity of either its premises or its conclusion. It is instead a comment about the fact that the premises would not support the conclusion even if they were true. Fallacious arguments may be of any of the following sorts:

In other words, if an argument is fallacious all the possible combinations of truth and falsity remain open.

There are indefinitely many arguments that people could present, but we do not have to approach each and every argument on its own, as being absolutely unique. Typically, arguments will be of some particular kind, and we will evaluate them by using the criteria relevant to arguments of that kind. What primarily enables us to sort arguments into kinds is the fact that many particular arguments share the same structure or, as we shall say, have the same form.

Consider the following two arguments:

The subject matter of these two arguments is quite different, but if you look at them closely you should see that they do share the same structure, have the same form. We could represent this form as follows:

As we shall later show, any argument with this form is a valid argument.