If you've ever spoken to someone with Alzheimer's, or certain kinds of very severe cognitive disorders, it becomes clear that language fluency tells you little

If you've ever spoken to someone with Alzheimer's, or certain kinds of very severe cognitive disorders, it becomes clear that language fluency tells you little to nothing about effective cognition. There are people who can't add 1+1 who can babble about random stuff convincingly, for a while, anyway, unless you're probing it.