If a beginner had only one book to study chess from, what book would you recommend it be?

"Chess: 5334 Problems, Combinations and Games" by Laszlo Polgar.

This assumes that the book is the only thing they have to study chess from. If they have other things, like access to the internet or even a coach, then they can probably get by just fine with no books.

many reasons, but as beginners become better later on, they'll found out that many OTB games are decided / lost in the endgame.

Play Winning Chess, by Yasser Seirawan.

@#10 I don't think an opening book makes sense. You can get a position that isn't lost after 10 moves by playing conservative developing moves, most of the time, and learning from your mistakes when that goes badly.

When I say tactics book, I mean a book of tactical ideas and motifs, not a book of puzzles. As many have pointed out, the internet has plenty of puzzle solving chances. I mean something like like Art of Checkmate or How to Beat Your Dad at Chess. Something to help you learn and recognize typical patterns. You'll get that eventually off hours of puzzles, but a primer is fine.

I also agree that endgames teach you a lot about the strengths and weaknesses of pieces, tempo, counting, calculation, etc. Endgame study before opening study for sure.

What about "the 300 most important positions written" by Lev Alburt ?

@StoppedClock "I don't think an opening book makes sense. You can get a position that isn't lost after 10 moves by playing conservative developing moves, most of the time, and learning from your mistakes when that goes badly."

You're completely wrong. First of all you have to teach beginners what "conservative developing moves" really are. You have to teach them natural developing squares for certain pieces and also nasty opening traps. Without this basic knowledge there is no way the kind of beginner player you mentioned would even make it that far into the game. His position would simply be dead lost until he could even make any use of his "endgame technique". Especially traps like scholar's mate which is extremely common for beginners. There is absolutely no use for any endgame skills when you fall for such kind of openings.

No doubt: Openings > endgame (at least for beginners)

@ClujMahal You are completely wrong.
A beginner should just know the opening principles, no need for any book. There is no point in teaching opening traps.
The most you can get out of heavy opening study is an advantage of 1 pawn. It takes considerable endgame skill to convert that to a win.
Many beginners go for traps. If an opponent falls into the trap, they gain a piece. Then they do not know how to win.
Scholar's mate is stupid. If you just think a few seconds about your move, then you do not fall into that. Most beginners play too fast in the opening.

No doubt: endgame > opening at any level below 2300 rating

@tpr it's quite funny that you're assuming every beginner will make it always into the endgame. But I do guarantee you, EVERY beginner will make it ALWAYS into the opening of a game. In order to make any use of endgame study you HAVE TO make it into an endgame with at least decent winning/drawing chances (roughly even material or positional advantages). To convert that to a win, as you mentioned. There is absolutely no point playing an endgame when being down 3 pieces/queen or what ever how much material. As long as there is just one pawn left on the board that is able to queen, he'll simply do it that way.

1. d4 d5 2. c4 dxc4 3. e3 b5 4. a4 c6
5. axb5 cxb5 6. Qf3 1-0

I've had this particular position against beginners many times and as you can see you win far more than just 1 pawn right out of the opening. This position is just completely winning for white after only 6 moves. Everything resulted out of a lack of opening theory.

@tpr
@ClujMahal
I hope that your interesting discussion wil give some clues to Findanegg !

@Sholmes49 the advice to @findanegg is an endgame book.

@ClujMahal 5...cxb5? is a blunder and should be 5...b4. That is not a lack of opening theory, it is a lack of thought. Without knowing any opening theory and just thinking "What will white do after I capture 5...cxb5?", the threat of 6 Qf3 is not that difficult to find. No amount of opening theory can substitute own thought. However much opening theory you know, there always comes some point when you are on your own. If you need memory as you cannot discern threats in the opening, then you will be lost in the middle game as you will need to be able to discern far subtler threats without any memorized help.
As Nimzovich put it:
"Opening theory is ballast"

Endgame study is useful even if you never reach an endgame. It teaches you to play chess.
As Capablanca put it:
"The opening is to prepare the middle game;
the middle game is to prepare the endgame."
In the endgame you learn how to play, what the value of the pieces really is, what positions are strong and weak.