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- Date: Tue, 12 Jan 1993 12:16:07 EST
- Sender: "Control Systems Group Network (CSGnet)" <CSG-L@UIUCVMD.BITNET>
- From: mmt@BEN.DCIEM.DND.CA
- Subject: Re: oughts on explanation
- Lines: 61
-
- [Martin Taylor 930112 12:00]
- (Bill Powers 930110.1900)
-
- >Quick note to Gary Cziko and Avery Andrews (930110 or some such)
- >Explaining how a music box works could go like this:
- >1. Turn the key until it won't turn any more.
- >2. Open the lid; this causes the music to play.
- >3. To stop the music, close the lid.
- >4. If the music stops by itself, return to step 1.
- >5. The above explains how the music box makes music.
- >
- >Or like this:
- >
- >The key on the music box winds a spring. When the lid is opened,
- >a catch is released and the spring turns a drum with little pins
- >sticking out of it. The pins bend and release flat springs, each
- >spring making a different sound. This explains what causes the
- >music to play.
- >....
- >In each case, the second set of explanations is couched in terms
- >of the way a system is currently organized, while the first is
- >couched in terms of antecedent events. The first type of
- >explanation is descriptive; the second generative.
-
- There's a more general way of looking at the two descriptions. The first
- one relates only to music boxes, whereas the second deals with objects
- whose properties are known to the student/listener/trainee (SLT) in other
- circumstances. The SLT is presumed to know what a "spring" is and does,
- so the only new information brought to bear is that there is one in the
- music box, and it can be wound (also a known concept) by the key. Springs
- are known to unwind unless held by something, so the new information is
- only what the detainer is. And so forth.
-
- The information in the numbered set of instructions cannot be used outside
- the world of music boxes. It would be effective with a mechanical moron,
- if the intention were to allow the moron to play the music box. The second
- would be useless with the moron, since it depends on the SLT having a good
- idea as to the mechanical and acoustic functions of many different things.
- To someone with that knowledge, the second set of descriptions provides
- rather less information about the music box as such than does the first.
- But it integrates the music box into a wide range of other tools and
- instruments (such as clocks and tuning forks. It doesn't "explain" why
- or how the box produces music. It only says that if you can explain why
- a clock works or why a tuning fork works, you can explain why the music
- box works. But can you "explain" those things? I think not. You can
- only relate them to other things.
-
- What you call "explanation" I would call description in terms of concepts
- with a range of applicability beyond the immediate problem, and particulary
- in terms of concepts already understood in some way by the SLT. The main
- point about "explanation" is that it uses a great deal less information
- or encompasses a much wider range of applicability than does "description."
- I see no qualitative difference between the two concepts, only a quantitative
- difference.
-
- The same is true of "descriptive" vs. "generative" models. Generative models
- provide descriptions over a much wider presumed range of applicability,
- and often use fewer independent pieces of information (using the term
- colloquially) to do it.
-
- Martin
-