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Monday, November 24, 2008

The Nature and History of Logic

This post won't do its title justice. I'm not going to delve too deeply into the nature or history of logic. But I want to paint a general picture of how I understand the topic, because it came up in a discussion I've been involved with on another blog.

The question was raised, If there are no minds to recognize the laws of logic, do the laws of logic still exist?

If there are no systems which instantiate the rules of inference, then the rules of inference do not exist.

When something exists that does instantiate the rules of logic, then the rules of logic exist.

I wouldn't assume that human brains are the only systems capable of instantiating the rules of logic, of course.

Now, consider how mundane my point here actually is. What I am saying about logic can be said about anything at all. Like apples, for example.

If there are no entities which structurally correspond to what we call "apples," then there are no apples. It is conceivable that we could live in a universe in which all apples have ceased to be. Yet, apples could grow again.

Thus it is with logic, and even tomatoes.

But why do brains instantiate the rules of inference? How do they do it? And, how did we figure out the rules in the first place?

As for the first question--why we use logic--I think the answer is evolutionary in nature. I don't have an ultimate understanding of how it happened that brains evolved to instantiate logic, but I see no reason to think that the answer to this question will forever remain outside of scientists' grasp.

As for the second question--how it works--again, I don't have an ultimate understanding, but I see no reason to think that neuroscientsts and cognitive scientists won't figure out all the details one day.

As for the third question, I wouldn't say we've figured out all of the rules of logic. The fact is, there may be an infinite number of possible logical systems. We've developed a good many logics, but we haven't discovered all of them. (This is not to say that the others actually exist in some non-physical realm. Rather, it is to say that they exist only as possibilities.)

But how did all of this happen?

First, we evolved the ability to use language. Then we were able to develop metalanguages--languages that allowed us to observe the defining characteristics of language itself.

Language is, of course, a tool. With the development of language came the development of abstract reasoning. And with the development of abstract reasoning came the ability to reason about reasoning. Thus it was that the first attempts at logic were made.

More advanced logics have explored many of the possibilities abstract reasoning affords, and I wouldn't assume that the full potential of reason will ever be exhausted.

Some claim that we cannot account for logic by reference to the physical world alone. They say some spiritual or non-physical realm must be conjured to explain it. If anybody can do a better job of explaining these things by postulating some non-physical realm, go for it. However, so far I haven't seen anyone describe a non-physical realm in a way that made sense. So far, talk about non-physical (or "supernatural") realms is incoherent, because there are no means provided which would allow us to tell the difference between one realm and the next, and there is no explanation for how these two supposedly different realms interact or relate to each other.

I don't have all the answers about how logic came about on planet earth, but my view makes sense and it is line with the evidence. I don't see any plausible or coherent alternatives on the table. So I'm sticking with the evolutionary model until something better comes along.