Why did he write it up so badly? He could make his arguments so much clearer if he just stated them fully. Maybe this piece was meant for math PhDs, not a general audience. To me, it comes across as an attempt to impress the reader with the semblance of authority and knowledge, not to guide the reader through the reasoning. This style of writing is often used to hide bad reasoning, to gloss over weak arguments or deliberately deceive. He could have done a better job.
He wrote it badly, because his goal is to write something controversial, which will remind people of his existence and hopefully increase the books sales. The target audience are people who are already his fans, and will accept uncritically anything he writes.
It is possible to have a reasonable debate about whether intelligence is real, what exactly it means, and what outcomes it correlates with. This is obviously not the way to do it. This is pure clickbait, pretending to be smart math, because pictures with dots and number, plus textbook screenshots.
Some of the things he says make sense. But he exaggerates their importance, and completely strawmans his opposition. "If you want to detect how someone fares at [X], make him/her do that task; we don’t need theoretical exams" - thank you, Captain Obvious!
I believe it was a twitter thread that he unrolled and mashed up into a medium post. On twitter he's often abrasive and kind of a dick as a character, and the tone carried into this post. He's doubled down about it because his rant seemed to have angered a lot of people among his demographic following, so if you follow him you'll probably find more explanation.
>this piece was meant for math PhDs
Lol it is absolutely not meant for math PhDs. I think anyone with a bachelor degree could follow the math (probably, I don't know much about the university system works in the US).
