When people talk about general intelligence in humans, they tend to talk about measured IQ. While a lot of variation in IQ is really just variation in brain health, and probably related to variation in general health, there are at least two distinct modes of general intelligence in humans: fluid intelligence and crystallized intelligence.
Fluid intelligence is pretty much anything you can use a spatial metaphor to think about, and is measured pretty directly by Raven's Progressive Matrices. It's used for puzzle-solving.
Crystallized intelligence, on the other hand, relies on your conceptual vocabulary. You can do analogical reasoning with it – so it lends itself to a fortiori style arguments.
I don't think it's just a coincidence that I know of two main ways people have discovered disjunctive, structural reasoning – once in geometry, and once in the courts. Continue reading