a finger pointing at the real thing.
I don't care much about causality.
???
To the extent that you view g as what it is, I have no problem. But people think g is (a) a real thing and (b) causal. It's not at all clear it is either. "Real things" involved in human intelligence are super complicated and have to do with brain architecture (stuff we really don't understand well). We are miles and miles and miles away from "real things" in this setting.
The game I was describing was how PCA works, not stuff in Pearl's book. The point was PCA is just relying on a model of a joint distribution, and you have to be super careful with assumptions to extract causality from that.
I think of g as, basically, a projection from the high-dimensional space of, let's say, mind capabilities into low dimensions, in this case just a single one. Of course it's an "artifact", and of course you lose information when you do that.
However what I mean by g pointing a finger at the real thing is that this high-dimensional cloud has some structure. Things are correlated (or, more generally, dependent on each other). One way -- a rough, simple way -- to get an estimate of one feature of this structure is to do IQ testing. Because it's so si...