Probably just not part of chess.com's copy of Stockfish's opening book.
Game Review Not Classifying Opening Move
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Jan 4, 2024
0
#3
GMegasDoux wrote:
Probably just not part of chess.com's copy of Stockfish's opening book.
I see, but this doesnt answer why it works on my phone and says its a book move, yet not on the PC, maybe specific version of stockfish?
Jan 4, 2024
0
#4
MagMalol wrote:
GMegasDoux wrote:
Probably just not part of chess.com's copy of Stockfish's opening book.
I see, but this doesnt answer why it works on my phone and says its a book move, yet not on the PC, maybe specific version of stockfish?
Just because something is a "book move" doesn't make it "not a mistake".
All that a "book move" means is that it can be found in ECO. Even in the old hardcover ECO books from the 80s and 90s (except "B", which was updated recently) had a few lines in them assessed as "+-", which means White is winning. There may have also been a few ultra-rare -+ scenarios.
Yes, a "book move" can very well be a mistake! Also, a book move could be from the 1980s and may have been "ok" then and since then outright refuted. I would bet that is the case for many lines of the second half of C40. C40 is 1.e4 e5 2.Nf3 and now all responses except Nc6, Nf6, and d6. The whole second half of it is 2...f5, the Latvian Gambit. Many sources now give 2...f5 a ?.
Theory evolves. "Book Move" and "Sound Move" are NOT synonymous!
Jan 4, 2024
0
#5
ThrillerFan wrote:
MagMalol wrote:
GMegasDoux wrote:
Probably just not part of chess.com's copy of Stockfish's opening book.
I see, but this doesnt answer why it works on my phone and says its a book move, yet not on the PC, maybe specific version of stockfish?
Just because something is a "book move" doesn't make it "not a mistake".
All that a "book move" means is that it can be found in ECO. Even in the old hardcover ECO books from the 80s and 90s (except "B", which was updated recently) had a few lines in them assessed as "+-", which means White is winning. There may have also been a few ultra-rare -+ scenarios.
Yes, a "book move" can very well be a mistake! Also, a book move could be from the 1980s and may have been "ok" then and since then outright refuted. I would bet that is the case for many lines of the second half of C40. C40 is 1.e4 e5 2.Nf3 and now all responses except Nc6, Nf6, and d6. The whole second half of it is 2...f5, the Latvian Gambit. Many sources now give 2...f5 a ?.
Theory evolves. "Book Move" and "Sound Move" are NOT synonymous!
Thank you for the in depth response, basically clears this up completely for me. As i said in the original post, i completely understand that the move itself according to an ENGINE is a mistake. I 100% understood that, my only example was eg. Benko Gambit, where even though it is also like +1.5 for white, all the moves are still book moves. But thanks for clearing this up 
Long story short. I recently started playing the Jaenisch/Halibut gambit against the English. Chess.com have an opening book for this, which can be found here: https://www.chess.com/openings/English-Opening-Jaenisch-Gambit
However when in games (unless on my phone for some reason???) it instantly classes b5 as a mistake. I understand as is, it isnt a great move, but it is a book move, that is classifying itself as a mistake.
Just wondering if anyone knows why this is? Other gambits i play eg. Benko Gambit and Scotch Gambit, both have plenty of book move classifications throughout the lines. Im just wondering why the FIRST move in this line is classed as a mistake, cheers