Logic vs. Rhetoric

By Steve Humphrey
Illustration by
Andrea Hutchinson

For many, the claims made by “scientists” are just part of the cacophony of voices telling us what to think and feel. Why listen to scientists? Why not artists or politicians or athletes? In this and future columns, I will try to explain just what science is, what its limitations are, what justifies the claims made by science and explain why the other voices do not warrant the same level of belief.

My name is Steven Humphrey. I have a Ph.D in the history and philosophy of science with a specialty in philosophy of physics. I teach classes in these subjects at the University of California, Santa Barbara, and have taught them at the University of Louisville. I have learned many things in over 30 years of teaching, the most important of which is how to communicate these sometimes complex ideas in ways that are accessible to the general public. I plan to do just that in these columns.

Let’s start at the beginning, which was in Greece some 2,500 years ago.

The pre-Socratic philosophers (some old guys in togas) recognized the difference between believing a proposition and that proposition being true. That is, it is possible for people to have false beliefs. (Duh!) So, in arguing for some position, one can use methods designed to convince or methods designed to reveal objective truth. The former art is called “rhetoric” and is used today by politicians, advertisers and lawyers. The latter is called “logic” and is used by scientists, mathematicians and engineers.

Some patterns of argument used in rhetoric are so emotionally compelling and persuasive that they were given special names. Logicians call these the natural fallacies; fallacious because though effective at influencing opinions, they are irrelevant to establishing truth. Examples include against the man (“his position must be incorrect; look at that haircut!”), appeal to the masses (“Everyone believes this, so why don’t you?”), appeal to pity (“Consider this wretched person; surely, he deserves a large cash settlement.”) and argument from authority (“If Beyonce says it’s true, it must be.”).

Logic, on the other hand, provides a way of establishing that one proposition follows from, or is implied by, other propositions in an independent, objective way. For example, if it is true that all cats are mammals, and that my pet Olivia is a cat, then it follows necessarily that Olivia is a mammal. This is an example of deductive logic, and it was first codified by another guy in a toga, Aristotle (384-324 BCE). The Greek Philosophers flourished in a society that was wealthy enough to allow some people to spend their time thinking and teaching rather than farming or trading or hunting, and these Philosophers were inventing and investigating ways to think about the world. And, just to demonstrate that things weren’t all that different, Socrates was condemned to death for “corrupting the youth of Athens.” Nowadays, he would just be slammed on Twitter.

The main take-away from this column is to recognize the difference between believing a proposition (even ardently) and that proposition being true. The history of science is really the story of the gradual abandonment of popular beliefs that seemed intuitively obvious. In my next column, I will talk about what “truth” means. V