Clerestory

Fluid and Crystallized Intelligence

October 03, 2019

I recently learned about the distinction between fluid and crystallized intelligence. The former sounds something like induction, thinking on the fly, comprehension, problem-solving, and learning, while the latter is about making deductions, and using accumulated knowledge. Studies have shown that the former peaks around 20, while the latter can in principle increase indefinitely.

It was mentioned in an offhand way on some podcast, possibly Sam Harris’ conversation with Judea Pearl. The idea that there is an age-determined apex has been bothering me since then, for a few reasons.

One seems obvious: I’m over a decade older than the proposed peak, and unlikely to reclaim much youth. So perhaps I’m naturally resistant to the idea that I’m in cognitive decline. Interestingly, though, I do know a few very intelligent people around my age who feel that they did peak at 20. (Though we disagree on whether we’ve peaked, we do agree that it’s not a happy prospect.)

But what bothers me more is that fluid intelligence doesn’t just refer to “raw compute,” at which I might (grudgingly) admit I’ve regressed. Learning and comprehension, too, I might be persuaded were easier, once upon a time.

But the idea that I’m worse at induction runs quite contrary to my experience. Personally, I don’t just feel that I know more than I did when I was 20, but that I am better at making abstract connections, even ones which depend on induction. (Then again, the wikipedia page lists analogies as relating to crystallized intelligence, so maybe what I’m referring to really is part of that more resilient part of intelligence.)

Or maybe I am worse at induction than I was then. It’s hard to say, given how hard it is, with my ageing brain, to remember what happened last week.

Anyway, the podcast made me wonder whether we hadn’t been discussing different kinds of intelligence, my friends lamenting one crumbling capacity, and I assuring them they could and should expect to grow sharper—in another.


I'm Bryan Kam. I'm thinking about complexity and selfhood. Please sign up to my newsletter or see more here.