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Teaching Argument: Using Deductive Logic

Walter Sinnott-Armstrong's Philosophy 3

Philosophy 3 is a course in Logic and Argument, offered to students at all levels. While it is not, in its current incarnation, a "writing course" (the course requires only one paper), it stands as an excellent illustration of how students might be taught the fundamentals necessary to the successful analysis and creation of arguments.

The course, as Professor Sinnott-Armstrong teaches it, is divided into three different sections. In the first two weeks, students are taught how they might analyze arguments by translating them into a standard form—that is, they transform prose into premises and conclusions so that they can understand, in very clear terms, the argument that is being presented.

Before this work can really begin, though, students must also understand some of the "slippery" qualities of language—for example, they must be able to analyze a statement not only for what it says, but also for what it implies. In these weeks, students are taught to look behind what someone is literally saying and to see what other meanings a speaker might intend.

Students will spend the next few weeks learning how to break down arguments into their component parts, identifying premises and conclusions throughout an argument. In order to facilitate this process, Professor Sinnott-Armstrong likes to give students transcripts of speeches on a matter that no one really cares about—for example, whether the members of the House of Representatives should be allowed to increase the number of clerks they have working for them. These kinds of texts tend not to rouse emotion and so make logical analysis easier.

Using these texts, Professor Sinnott-Armstrong models for students how to put an argument into its standard form of premises and conclusions. Students also label the rhetoric in each sentence according to the terms that they have been learning. Students then come to understand the many things going on within a paragraph and within language itself to make an argument persuasive. Texts employ assumptions and deflections, declarations and rhetorical devices that together add up to make the argument. When students put an argument into standard form they can really see what the writer is arguing.

Once all of the explicit premises are stated in standard form, Professor Sinnott-Armstrong instructs his students to look for the implicit or suppressed premises: "Well, if the speaker says A, he must be assuming B, taking C for granted. Why doesn't he come right out and state his premise? Either he knows that everybody already agrees with his premise, or he is trying to suppress a premise that is very controversial." In this way, Professor Sinnott-Armstrong equips his students with the tools of analysis.

So far, students have been shown how to analyze (or break down) an argument. The second part of the course teaches students how to evaluate argument, both deductively and inductively.

First, students are taught how to test an argument for deductive validity—that is, for whether the conclusion follows from the premises. Students are here introduced to the terms "validity," "truth," and "soundness"—noting that an argument might be valid (in that the conclusion does indeed follow from the premises) without being sound (which also requires that the premises are true). Students must carefully probe each premise to determine its truth before they can declare an argument sound.

After showing students how to evaluate a deductive argument, Professor Sinnott-Armstrong devotes a couple of weeks to evaluating inductive reasoning. Here, students are presented with arguments that are not deductively valid, but that still provide convincing reasons to believe their conclusions. Students discuss these reasons, weighing their strengths and weaknesses, thereby evaluating the argument at hand. They also examine the argument for any of the logical fallacies—such as equivocation, begging the question, and so on—that can undermine an argument's validity. By the end of this part of the course, students are well equipped to evaluate any argument—deductive or inductive.

In the final section of the course, Professor Sinnott-Armstrong instructs his students in the process of constructing an argument. Here, Professor Sinnott-Armstrong assigns articles that are for and against controversial positions, such as abortion, affirmative action, whether machines can think, what killed the dinosaurs, and so on. Students are asked to take a stand on these controversial matters and to write an essay in which they construct the best argument that they can. When they've finished, students then write an analysis of their own arguments, breaking them down into the premise-premise-conclusion model that they learned in the first weeks of the class. Professor Sinnott-Armstrong then evaluates students' arguments, pointing out where they commit a fallacy, overlook possible objections, ignore needed qualifications, and so on.

This method of writing instruction has some real benefits—especially in terms of coherence and clarity. Making students aware of the components of their arguments helps them to keep track of how these components work together. Organization tends to be better at the paragraph and sentence levels, and irrelevancies and redundancies tend to disappear—two important benefits of training in informal logic.

Last Updated: 8/10/08