Chess/Tempo

Each turn is a precious commodity, which we call a tempo (Italian for 'time'). A tempo is an opportunity to move something.

Chess is a turn-based game, so you might think that Black always gets one tempo for every tempo White gets.

Not quite.

If you can make an improving move, like a developing move, in a way that makes your opponent react by doing something they'd rather not do, like move a piece twice in the opening, you have gained a tempo on them.

White and Black sit down at a chess board and start playing. After 1. e4 e5 2. Bc4, White's bishop attacks the weak f7-pawn. It's now got one attacker and one defender.

Black continues 2...Bc4 and White plays 3. Qh5. The queen attacks both f7 and e5. That's two attackers on f7, and still only one defender (see diagram).

If Black defends the f7 pawn with 3...Nh6?, then White can take the e5 pawn with check, 4. Qxe5+. If Black plays 3...Nc6?? to defend the e-pawn instead... White would play 4. Qxf7#. The # stands for checkmate. Oops! So instead Black plays a move that defends both f7 and e5: 3...Qe7.

White's attack thwarted, let's say they now play 4. Nc3. But, what does White's queen think she's doing on h5? Everything she can attack is defended. She can't make any more progress. If she was a hockey player, she would be offside.

But more importantly, Black is going to play 4...Nf6 next and gain a tempo on the queen. (diagram)

Chess is a turn-based game, and you can only move one piece each turn (except when castling). So, if your queen is doing something this turn, bad luck, the rest of your pieces have to stay put. In business-speak, there's an opportunity cost to moving the queen.

White reverses the queen back to 5. Qf3. Now it's Black's turn again, and they have a chance to make another useful move, like 5...Nc6. Black now has more pieces developed than White.

Through tempo magic, it's almost like Black got to make two moves in a row.

It's hard to overstate how powerful that is. This is how Larry Evans, a grandmaster and prolific chess author, described it:

The first question a good player asks when he looks at a position is: “Whose move is it?” Time is so vital that if a player with only mediocre ability were allowed to move twice in a row, at his option, just once in every game, he could become World Champion!

—Larry Evans^[1]

	a	b	c	d	e	f	g	h
8									8
7									7
6									6
5									5
4									4
3									3
2									2
1									1
	a	b	c	d	e	f	g	h

Knight attacking a pawn

You gain tempi when you attack a piece with a developing move and the opponent can not defend the piece with a developing move, so she or he loses tempi.

	a	b	c	d	e	f	g	h
8									8
7									7
6									6
5									5
4									4
3									3
2									2
1									1
	a	b	c	d	e	f	g	h

Knight attacking the queen

You lose tempi when your opponent attacks your piece with a developing movement and you cannot defend that piece with a developing movement, so you have to spend one tempo by retreating your piece or defending it (with a non developing move).

1. ↑ Evans, Larry (1974). "Basic Chess Strategy". How to Open a Chess Game. New York: RHM Press.