Thursday, August 28, 2008

Substances and artefacts

[Catapults]Let us suppose that I am playing a nice game of Xiangqi with my daughter. The pieces are wooden, with painted red or black characters. As we play, we notice that one of the red catapult pieces has the character on its surface half warn off. So, I grab a laser pointer, and some motors, and a little processor, and program the motors to move the laser pointer rapidly so as to trace out the missing half of the character drawn on the piece, indeed to do so so rapidly that it looks like the character is all in place without any flicker. Moreover, I add a little camera that tracks the wooden disc, and continually repoints the whole assembly to follow the disc, so that when I move the disc, the character drawn on it moves with it. As we keep on playing (maybe the paint on the piece is of very low quality), more and more of the character wears off, and I am continually reprogramming the motors to replace more and more of the paint by the laser beam. Eventually, the disc has no paint on it, but has a laser image of the catapult character on it. I then take a bite out of the wooden disc itself. (Maybe I'm a beaver.) And I keep on taking more bites, while reprogramming the laser beam not to track what's left of the wooden disc, but to track my finger motions. Finally, I finish eating the wooden disc. I can now finish the game of Xiangqi with my daughter, except that now one of the red catapult pieces has become a pattern of laser light.

Suppose we were tempted to say that the initial red catapult piece was a substance.[note 1] Now, surely, a pattern of laser light isn't a substance. Light-spots aren't even processes, but quasi-processes. They can, after all, "move" faster than light.[note 2] So then we have the oddity that a substance became a non-substance. But it is plausible, for the same reasons for which it is plausible to suppose that the Ship of Theseus survives the replacement of its parts, that the red catapult piece survives its replacement with a light spot. Thus, if the red catapult piece initially was a substance, then one and the same thing is an existent substance at t0 and an existent non-substance at t1. Moreover, this didn't take any kind of miracle—all it took was a bit of skill with motors and electronics. If this seems absurd to you, then you may wish to conclude that the initial red catapult piece was not a substance.

Similarly, a painting could be restored with new paint, or it could be repaired piece by piece by projected light. A chair could be replaced, piece by piece, with force-fields, perhaps, or maybe even with carefully aimed jets of air. A computer could be replaced, piece by piece, with an emulation of itself (just replace the parts one-by-one with emulations). If these things survive this kind of replacement, and if we do not wish to accept that there can be change between categories—that a substance can change into a non-substance, say—at least without a miracle[note 3], then the conclusion to draw is that Xiangqi pieces (and by the same token international chess pieces), paintings, chairs and computers are not substances. In fact, it seems plausible to generalize this: perhaps no artefact is a substance, unless perhaps it is wholly composed of one non-artefactual substance (such as Peter van Inwagen's example of the hammock that is made out of one snake, weaved into a hammock like a rope).

Some of us want to go one step further, and deny that artefacts, except perhaps if wholly composed of one non-artefactual entity, exist. For it is not implausible to say that spots of light don't exist, and anything that can change into a spot of light doesn't exist either.


N said...

Dear Alex,

There are two issues that might be interesting to address.

1. Does the part of the pattern which you replace with laser light early in your first para have different persistence conditions from the rest of the game piece? If you get your hand in the way of the laser pointers, that part of the pattern disappears, but the rest does not. Does this tell us anything about the unity of the piece plus light supplement?

2. Can one of your game pieces become a 'pattern of laser light' as you suggest? I have seen 3-D representations of things formed by light in films (such as Star Wars), but not in real life? Would the pattern not have to be projected somehow onto an appropriately contoured 'backdrop'. Given Aristotle's definition of a primary substance as something that does not depend for its existence on anything else, this may suggest that something has gone wrong.

What do you think? Or are these minor issues?

Enigman said...

Maybe I'm a beaver.

Well, your body could be changed bit by bit into the body of a beaver, and even now you share much in common with a beaver, but that does not make even your body now a beaver's body...

one of the red catapult pieces has become a pattern of laser light

Or was one of those pieces gradually replaced by a pattern of light?
That there seems to have been a becoming could be due to the functional role of the piece. Perhaps you were (at least partially) referring to a fictional object (within the fiction of your scenario) rather than to a wooden piece - and it would not matter to the game how that fictional object was instantiated.
After all, suppose that matter is made of strings, and that such strings vary in ways that make no difference to observable physical properties, as well as in the physically interesting ways. The former sort do not seem to affect reference, the latter might. If water changes from H2O to XYZ then it makes a difference, but if the stuff of the H and the O change without that making any chemical difference then it does not make a difference to reference either.

Alexander R Pruss said...

I think one could take a statue made of bronze and gradually replace the bronze by a plastic with the same outside coloration, and the statue would survive this, as long as being-made-of-bronze were not essential to the artist's intentions here. Sometimes the precise material, and not merely its appearance, that a work is made of is essential to the artist's intentions. Thus, it may be artistically essential to a medieval illuminator that real gold be used for a halo, because of the symbolic power of gold. Or, for a very different example, it may be artistically essential to a contemporary painter that one particular bodily fluid be used.

However, the woodenness of Xiangqi pieces does not seem to me to be essential in the same way. If I replaced the wood in the piece gradually with plastic, while continuing to play the game, I think I would still have the same piece. But what is more controversial, and on which this argument rests, is that just as I could replace the wood with plastic, so too I could replace the piece with something that doesn't exist at all!

Alexander R Pruss said...

If I grab the lasered piece from above, the character appears on my hand rather than on the piece! Presumably these problems could be fixed with a little bit more technology.

Enigman said...

But why not say, rather pragmatically, that the artifact exists, but that its identity conditions are fuzzy (not that unlike how all the meanings of our words are, after all)?

...e.g. chairs exist, and this chair that I am sitting on exists. I could sit on a chair that was a work of art, a modern sculpture such as you describe - such that the possible eventual virtual chair would be the same chair (in some sense) - but that I would count as one chair (a physical continuant) amongst the few in this room nonetheless (I would be presuming that none of those chairs were identical time-travelling chairs, of course).

Incidentally, the Stranglers did something once called 'Aural Sculpture,' and a piece of music can be made more obviously not only of air vibrating in a concert hall, to which tickets are sold, but also plastic, when sold as a recording; or it could be made of practically nothing, in the case of the information being downloaded from the internet. So one could be listening to Aural Sculpture from a record, and have the input to the speakers gradually changed to a download...

A bit like seeing a mirage, walking closer to it and having your view of it gradually changed into a view of the real oasis originally hidden behind the mirage?