Daniel Dennett on Reductio ad Absurdum, the Philosopher's Crowbar
Philosopher Daniel Dennett discusses reductio ad absurdum, "the workhorse of philosophical argumentation," wherewith thinkers test the validity of an opponent's argument by taking it to its most illogical extreme.
Daniel C. Dennett is the author of Intuition Pumps and Other Tools for Thinking, Breaking the Spell, Freedom Evolves, and Darwin's Dangerous Idea and is University Professor and Austin B. Fletcher Professor of Philosophy, and Co-Director of the Center for Cognitive Studies at Tufts University. He lives with his wife in North Andover, Massachusetts, and has a daughter, a son, and a grandson. He was born in Boston in 1942, the son of a historian by the same name, and received his B.A. in philosophy from Harvard in 1963. He then went to Oxford to work with Gilbert Ryle, under whose supervision he completed the D.Phil. in philosophy in 1965. He taught at U.C. Irvine from 1965 to 1971, when he moved to Tufts, where he has taught ever since, aside from periods visiting at Harvard, Pittsburgh, Oxford, and the École Normale Supérieure in Paris.
His first book, Content and Consciousness, appeared in 1969, followed by Brainstorms (1978), Elbow Room (1984), The Intentional Stance (1987), Consciousness Explained (1991), Darwin's Dangerous Idea (1995), Kinds of Minds (1996), and Brainchildren: A Collection of Essays 1984-1996. Sweet Dreams: Philosophical Obstacles to a Science of Consciousness, was published in 2005. He co-edited The Mind's I with Douglas Hofstadter in 1981 and he is the author of over three hundred scholarly articles on various aspects on the mind, published in journals ranging from Artificial Intelligence and Behavioral and Brain Sciences to Poetics Today and the Journal of Aesthetics and Art Criticism.
Dennett gave the John Locke Lectures at Oxford in 1983, the Gavin David Young Lectures at Adelaide, Australia, in 1985, and the Tanner Lecture at Michigan in 1986, among many others. He has received two Guggenheim Fellowships, a Fulbright Fellowship, and a Fellowship at the Center for Advanced Studies in Behavioral Science. He was elected to the American Academy of Arts and Sciences in 1987.
He was the Co-founder (in 1985) and Co-director of the Curricular Software Studio at Tufts, and has helped to design museum exhibits on computers for the Smithsonian Institution, the Museum of Science in Boston, and the Computer Museum in Boston.
Daniel Dennett: One of the reasons I wrote this book is because oddly enough, philosophers who are famous -- notorious for being naval gazers, for being reflective. I think, in fact, philosophers are often remarkably unreflective about their own methodology. I wanted to draw attention to how philosophers actually go about their business and get them thinking more self-consciously about the tools they use and how they use them.
A tool that everybody should be familiar with and, in fact, people use it all the time is reductio ad absurdum arguments. It's the sort of general purpose crowbar of rational argument where you take your opponents premises and deduce something absurd from them. That is, you deduce a contradiction officially. We use it all the time without paying much attention to it. If you say something like -- if he gets here in time for supper, he'll have to fly like Superman.
Which is absurd -- nobody can fly that fast. You don't bother spelling it out, you just say -- you point out that something that somebody imagined or proposed has a ridiculous consequence. Well, let's look at one of the great granddaddy reductio ad absurdum arguments of all times. And that's Galileo's proof that heavy things don't fall faster than light things leaving friction aside. He argued as follows.
Okay, suppose you take the premise that you're gonna show is false. Suppose heavier things do fall faster than light things. Now, take a stone A which is heavier than another stone B. That means if we tied B to A with a string, B should act as a drag on A when we drop it because A will fall faster, B will fall slower and so A tied to B should fall slower than A by itself. But A-B tied together is heavier than A by itself so it should fall faster. It should fall both faster and slower than A by itself. That's a manifest contradiction. So we know that our premise with which we began has to be false. That's a classic reductio ad absurdum. That's been known and named for several millennia I guess. And, as I say, it's the workhorse of philosophical argumentation.
Directed / Produced by Jonathan Fowler and Elizabeth Rodd
With his new book "Intuition Pumps and Other Tools for Thinking," philosopher Daniel Dennett offers a kind of self-help book for deep thinkers -- a series of thought experiments designed as a workout for the deliberative mind. Here he discusses reductio ad absurdum, "the workhorse of philosophical argumentation," wherewith thinkers test the validity of an opponent's argument by taking it to its most illogical extreme.
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