My beef isn't with Shalizi's reasoning, which is correct. I disagree with his text connotationally. Calling something a "myth" because it isn't a causal factor and you happen to study causal factors is misleading. Most people who use g don't need it to be a genuine causal factor; a predictive factor is enough for most uses, as long as we can't actually modify dendrite density in living humans or something like that.
Ok, let's talk connotations.
If g is a causal factor then "A has higher g than B" adds additional information to the statement "A scored higher than B on such-and-such tests." It might mean, for instance, that you could look in A's brain and see different structure than in B's brain; it might mean that we would expect A to be better at unrelated, previously untested skills.
If g is not a causal factor, then comments about g don't add any new information; they just sort of summarize or restate. That difference is significant.
A predictive...
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