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LG comments on Where to Draw the Boundary? - Less Wrong

36 Post author: Eliezer_Yudkowsky 21 February 2008 07:14PM

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Comment author: LG 22 February 2008 02:51:00PM 2 points [-]

"You can't judge the usefulness of a definition without specifying what you want it to be useful for."

This was going to be my point:

"Once upon a time it was thought that the word "fish" included dolphins. Now you could play the oh-so-clever arguer, and say, "The list: {Salmon, guppies, sharks, dolphins, trout} is just a list - you can't say that a list is wrong. I can prove in set theory that this list exists. So my definition of fish, which is simply this extensional list, cannot possibly be 'wrong' as you claim."

Or you could stop playing nitwit games and admit that dolphins don't belong on the fish list."

I totally see your point, but I think it's worth exploring why the "nitwit" set is plausible, and why you feel the best defense against a cheeky definition is is an ad hom.

In this instance, I think the answer is that you're drawing the boundary line for one reason, and they are being twitty and drawing the boundary line arbitrarily just because they think the rules of logic allow them to do so with impunity (ad hom away).

However, I can think of a legitimate reason to draw the boundary in the nitwit way: what if I want a label whose members are all creatures that live in water and use fins to propel themselves? That's a legitimate category, but it certainly isn't a boundary appropriate for the word "fish," which has taxonomical implications, as well as physiological implications more complex than "has fins."

It may be worth pointing out to the nitwit that he's drawn a logically valid boundary, but it's not the territory you're talking about. Allow him his Fishoids, but steer the conversation back to creatures who have gills and lay eggs. Ideally you can get away with convincing the nitwit to re label HIS category so you can use the real fish label to avoid confusion, but in the interests of continuing a productive conversation, you might consider relabeling the boundary you mean to something neutral ("Gill Creatures"), that your opponent won't be so comfortable changing arbitrarily.