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Society of Mind

12.11 how causes work

It's wonderful when we can find out something's cause. A tower is high because each of its separate blocks contribute height; it stands because those blocks are adequately firm and wide. A baby cries because it wants food. A stone falls down because it's pulled by gravity. Why can we explain so many things in terms of causes and effects? Is it because there is a cause for everything — or do we merely learn to ask only about the kinds of happenings that have causes? Is it that causes don't exist at all but are inventions of our minds? The answer is all of the above. Causes are indeed made up by minds — but only work in certain parts of certain worlds.

What are causes, anyway? The very concept of a cause involves a certain element of style: a causal explanation must be brief. Unless an explanation is compact, we cannot use it as a prediction. We might agree that X causes Y, if we see that Y depends more on X than on most other things. But we wouldn't call X a cause of Y if describing X involved an endless discourse that mentioned virtually everything else in the world.

There can't be any causes in a world in which everything that happens depends more or less equally upon everything else that happens.

Indeed, it wouldn't make any sense to talk about a thing in such a world. Our very notion of a thing assumes some constellation of properties that stays the same (or changes in ways we can predict) when other things around it change. When Builder moves a block, that block's location will change — but not its color, weight, material, size, or shape. How convenient that our world lets us change a thing's location while leaving so many other properties unchanged! This lets us predict the effect of motions so well that we can chain them into combinations never tried before — yet still predict their principal effects. Furthermore, because our universe has three dimensions, we can easily predict the effect of combining several actions from knowing only their effects in each of those three dimensions.

Why does a block retain its size and shape when it is moved? It is because we're fortunate enough to live within a universe in which effects are localized. A solid object with a stable shape can exist only because its atoms stick together so tightly that when you move some of them, the others are pulled along. But this can happen only in a universe whose force laws work in close accord with the nearnesses of time and space — in other words, a universe in which entities that are far apart have much less effect on each other than ones that are close together. In worlds without constraints like that, there could be no things or causes for us to know.

To know the cause of a phenomenon is to know, at least in principle, how to change or control some aspects of some entities without affecting all the rest.

The most useful kinds of causes our minds can discern are predictable relationships between the actions we can take and the changes we can sense. This is why animals tend to evolve sensors that detect stimuli that can be affected by those animals' own actions.