October 24, 2004

An informative tautology

Among the examples of true Bush tautologies cited by Geoff is:

If affirmative action means what I just described, what I'm for, then I'm for it." George W. Bush, during the third presidential debate, St. Louis, Mo., October 18, 2000
This is is actually an informative statement and doesn't deserve to be derided as a tautology. The reason that tautologies are derided is because they typically convey no information. Sometimes, however, they do convey information. In this case, what Bush is saying is that "affirmative action" means different things to different people and that he is in favor of some of them, and, implicitly, opposed to others. He's not alone in this. There are, for example, lots of people who favor such activities as recruiting of under-represented groups but oppose quotas.

In fact, there is a large class of statements that are technically tautologies but are nonetheless informative. These are statements that equate terms whose intensions are distinct but in fact have the same extension. Crudely put (since the details are the subject of on-going debate among semanticists and philosophers), the extension of an expression is the set of things of which it is true. The intension of an expression is the set of properties taken to be characteristic of it. The classic example of an informative tautology is "Hesperus (the evening star) is Phosphorus (the morning star)." This is a tautology since Hesperus and Phosphorus are both the planet Venus - the two expressions thus have the same extension. It is, nonetheless, informative, because the intensions of the morning star and the evening star are different and we learn something when we are informed that they are actually the same heavenly body.

Posted by Bill Poser at October 24, 2004 11:33 PM