I think of my brain1 as hosting a zoo of deeply nested structures that clump together in response to action in the world. When I encounter something new, whatever is in charge works quickly to find an appropriate structure; in fact, this is where it shines. The tool it uses to go from new to old—the glue that builds and connects structures—is analogies. These tend to be less the SAT Verbal variety (Fish:School::) and more like metaphors:
- "Sam is a funnier John"
- "This is the play we saw in practice, except for that move"
- "R3 is an infinite stack of infinitely large sheets of paper"
Analogies appear all over the place in more veiled forms. A good example is our everyday working assumption that other people think the way we do. Anytime we read a facial expression, we're implicitly mapping our world onto someone else's; to understand them we consult the best reference we have, namely, the huge store of structural information about our own behavior built from years of self-absorption.
And all kinds of familiar problems, like finding the men's room at a new restaurant, making small talk, or parsing the news can be solved by reference to well-known patterns. That way we avoid all kinds of redundant work, in much the same way that the eye works efficiently by (a) ignoring most of the picture and (b) locking onto movement.
This is not to mention, of course, the critical role of analogy in language. Turns of phrase, puns, cliches, transitions, etc., all exploit ready-made structures to help get an idea across. Like the phrase "get an idea across."
Yet as indispensable as it is, analogical reasoning has a major kink. Each of us has a limited set of things to make analogies to that depends critically on which structures were active most recently; consider how different the world looks after a good laugh or bad grade. The way we think, then, is necessarily shaped by what's in the cache at any given moment. This helps explain the kind of inertia that keeps people from thinking creatively or climbing out of a bad mood.
It also explains why people so often claim to be "streaky" or that they "either failed or aced the exam": interesting edge cases crowd out more frequent—but also more forgettable—scenarios. The brain is easily fooled by the illusion of structure. Just think of religion, racism, conspiracy theories, or rhetoric.
In fact, nearly every kind of evil can be seen in that light, as the byproduct of a particularly overactive structure set.1. Thanks to Douglas Hofstadter.