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Comment by bandrami | Hacker News Reader

Aristotle distinguished four kinds of answers to "why?" e.g. "why is this table flat?"

1. Material cause: because wood is rigid and holds its shape

2. Efficient cause: because the carpenter used a plane or chisel to carve away everything that was not that flat surface

3. Formal cause: because that's the blueprint the carpenter used

4. Final cause: because if it were curved your jug of wine would fall over

We can get material, efficient, and formal causes here (the algorithm being the formal cause) without any real controversy. But if I asked a human cryptographer "why is there an XOR in this round?" I'm asking about the fourth one, the final cause or purpose; the cryptographer might answer "because I wanted uncorrelated input bits to stay uncorrelated after this round", or whatever. But talking about that most interesting "why?" as regards an AI's activity is... controversial, to say the least.

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> if I asked a human cryptographer "why is there an XOR in this round?" I'm asking about the fourth one, the final cause or purpose; the cryptographer might answer "because I wanted uncorrelated input bits to stay uncorrelated after this round", or whatever. But talking about that most interesting "why?" as regards an AI's activity is... controversial, to say the least.

Really? We don't seem to have any problems with saying "your eyeball contains a lens to focus light onto the retina" or "predators have sharp teeth because that is the efficient way to handle meat, as opposed to fibrous plants", but those are both final causes. There's nothing different about an AI's activity. Any activity or quality that is pursuant to a goal, however defined, may have a final cause.

Plenty of evolutionary biologists would rant against that kind of language, though.

Evolutionary biologists are perfectly comfortable with the idea that focusing light is the purpose of a lens, and cutting meat is the purpose of sharp teeth, and structural support is the purpose of a skeletal system, etc. etc. etc. It's not fallacious in any sense. What they rant against is the idea that items with a purpose must have been ordained by a supernatural force.

No, answering a why question about an organism's structure with "because [purpose]" really does get a evolutionary biologist's goat.

Why do tigers have sharp teeth? To rip flesh.

No.

Why do tigers have sharp teeth? Because their ancestors who had sharper teeth produced more offspring than their relatives who did not.

In Aristotle's language, ripping teeth may be a cause, but it's not the Final cause, and that's what we're talking about.

The reason biologists don't like the teleological explanation is that (a) it tends to make people think of a creator, as you say, but also (b) it describes traits as "solutions" to specific "problems" (e.g. the problem of ripping flesh), but the issue is that, starting from the pre-sharp-toothed ancestor, there were infinitely many possible directions evolution could have taken that would never have needed to solve this "problem." The existence of the problem (cutting meat) and the random path that led to the tigers being carnivorous are actually one-and-the-same. If you didn't have sharp teeth, you wouldn't have needed them.

If you want to write more about this and publish it somewhere, I would read it.

Well, Aristotle did it better than I ever could (in "The Metaphysics", which isn't nearly as kooky as it sounds; it just means it's the second volume of "The Physics").

What I do really love about it (and this plays out in medieval European and Islamic thought, both of which were strongly influenced by Aristotle) is that he says that for a living thing, the formal cause and final cause are the same thing. The various motions and activities of an organism (this is all Aristotle meant by "soul") are its final cause; my living my life as well as I can is my purpose.

That applied to the whole cosmos, too. Aristotle considered the cosmos alive (after all, the stars and planets move without anybody pushing them), which meant the purpose of the cosmos was to be the way it is and spin those crystal spheres and epicycles they imagined the planets moved on. And that final cause, that universe's-motion-as-its-own-purpose, he called "God" -- the omega point that the universe moves towards. In the renaissance and enlightenment this got reversed, and the "first cause" came to mean first in sequence rather than importance; from that you get Newton's "watchmaker" God, which would have been incomprehensible to a medieval thinker (let alone Aristotle).

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