The Anatomy of an Argument

As the term is used in philosophy, an argument is a set of related propositions (called premises) that is given as a reason for believing a further proposition (called the conclusion). Consider, for example, the following, simple argument:

Whoever murdered Carl had to have access to his rose garden at midnight, and the only person who did was Natalie, therefore Natalie must be the murderer.

Here the conclusion is that Natalie murdered Carl, and there are two premises: (1) that whoever murdered Carl had access to Carl’s rose garden at midnight, and (2) that only Natalie had such access.

There are a few ways in which we can represent an argument that make its structure clearer. One popular way is called standard form. Here’s what the argument we have been discussing looks like in standard form:

1. Whoever murdered Carl had access to his rose garden at midnight. 2. Only Natalie had access to Carl’s rose garden at midnight.

3. Natalie murdered Carl.

Each proposition has been written on its own line and labeled with a number. The premises are written first, and a line is drawn to separate them from the conclusion. This line represents the inference—the mental act of moving in thought from the premises to the conclusion.

You will occasionally find arguments written out in this way in some of the readings for this class. However, we will be making more use of a newer way of representing the structure of arguments, which is called “argument mapping.” Here’s a map of the argument we’ve been discussing.