When it’s best to try to convince, rather than prove

(Reflections on Carroll C Arnold’s Introduction to Chaim Perelman’s “The Realm of Rhetoric”, University of Notre Dame Press, 1982).

When is it better to try for a convincing argument, rather than a conclusive one? And how would you go about that?

You should aim to convince, rather than prove, when your premises are disputable. That is, when you are dealing in the realm of “values” (as Perelman would say). I take it that this realm is bigger than it first appears: and would include decisions about most human social systems.

Argumentation that aims to convince can be termed “rhetoric”. Argumentation that aims at a proof, at a conclusion, can be termed “logic”. Logic can only be applied when your premises are indisputable. Beware of trying to apply logic into situations where your premises are open to opinion. You will end up with disparate and conflicting conclusions.

Rhetorical argument must have as its goal the “adherence” of an audience. Rhetorical argument, by the nature of the matters it deals with, will always have an audience. Even if that audience is just yourself. And its aim cannot be to get the audience totally signed-up to a claim. Rather, its goal can only be to increase the adherence of that audience to the claim. In the domains where rhetoric applies, we cannot hope for 100% acceptance of a claim. Only degrees of allegiance or adherence.

So, how do you argue in a good way, in the domains where your premises are disputable? That is, how do you argue rhetorically? One way to answer this is to draw analogies from the realm of logic: a realm we are more familiar with.

In logic, you build your argument from self evident premises. Premises that are universally true. In rhetoric, you need to build your argument from your audience’s knowledge and experience. You need to appeal to what they know. To what they value. To what they have gone through. You also need to take into account your audience’s current situation.

In logic, you rely on definitions of terms. Once a term is defined to mean a certain thing – its meaning is clear to everyone dealing in that formal system. For example, in the Tax Act, the term “assessable income” is defined in the “definitions” section of the Act. That term, “assessable income” will retain that defined meaning throughout the Act. Its meaning is not open to dispute by any accountant or judge.

In rhetoric, where you are dealing with language in an informal system (not the formal systems of logic), your language will always be ambiguous. You can’t pin a single definition down to a term. So, what can the rhetorician do? Her only option is to make her particular meaning of a word compelling to an audience. She must give her meaning of the word “presence” to that audience.

Finally, logic reaches its conclusions by following deductive steps in a formal proof. The logical rules, which allow you to advance from one step to the next, are well understood and universally agreed. No such formal rules exist for rhetoric. Instead, you need to make “liaisons” between ideas. You progress as you see and build the links between ideas. The rhetorician will use metaphor, examples and models to create these liaisons. She will also resort to argument by analogy, or by an appeal to the way things are (as viewed by the audience) to make these links.

Perelman’s contention, in the end, is that it's possible, in fact it's more intellectually honest, to aim for arguments that are “inconclusive” (in the logical, positivist sense) and yet still “convincing”.