[tuxiano]

I don't know the last one but I recall the matches of Hydra chess machine [0] in the early 2000s against GM Adams in tournament condition (5½ to ½ for the machine) and against GM Nickel in correspondence condition (2 to 0 for the human). Both Grandmaster were top players in their relative field so it showed very clearly how the time limitation impacted the competitive results. Nobody in the chess elite would claim that Hydra understood chess better than GM Adams but still he lost resoundigly due to the inevitable mistakes caused by the relatively fast time control.

[0] https://en.wikipedia.org/wiki/Hydra_(chess)

[JamesBarney]

But wasn't Hydra 2005 ~2800 ELO where as the current best chess engines like Leela Chess Zero or Stockfish are ~4000 ELO?

Just realized that correspondence chess is cyborg chess, I didn't know computers were legal in correspondence chess, but it makes sense now. Reading about it, it sounds like it's less about knowing chess, and more about understanding the applications you're using.

[tuxiano]

Chess engine ratings are not immediately comparable to human ratings as they are extracted from different pools. Hydra played relatively few games so its rating estimation was somewhat approximate but it was clearly "superhuman" (GM Adams was n°7 in the world and only scored one draw in 6 games). Today Stockfish is awarded a rating of about 3500 [0] with a typical PC hardware but this rating comes from matches between engines and not with humans.

Regarding the argument of "knowing chess", it depends on you definition. I often use this analogy. Correspondence chess is to tournament chess what the marathon is to track running. They require different skills and training but I guarantee to you that a lot of understanding is involved in correspondence chess, possibly more than in tournament chess.

[0] https://ccrl.chessdom.com/ccrl/4040/