Prophylaxis, or asking what your opponent wants

Most players choose moves by asking what they would like to do. The single cheapest improvement available at 1200 is asking the other question first.

From Nimzowitsch, My System, 1920s
Costs one tempo
The question what does my opponent want to play?

Prophylaxis is Aron Nimzowitsch's word, from a book written in the 1920s that most people quote and few finish. The idea underneath it needs no theory at all: before you play your move, work out what your opponent is planning, and consider spending a move to make it impossible.

It feels wrong at first because a prophylactic move usually looks like it does nothing. That is exactly what it is. The value is negative value, in your opponent's position, and it does not show up anywhere on your side of the board.

One quiet move that removes an idea for good

A quiet Italian. Both sides have developed sensibly and White has a small decision to make on move six.

1.e4 e5 2.Nf3 Nc6 3.Bc4 Bc5 4.c3 Nf6 5.d3 d6 6.h3

6.h3 develops nothing and attacks nothing. What it does is take g4 away from the black bishop for the rest of the game. Without it, Black plays ...Bg4 and pins the f3 knight against the queen; with it, ...Bg4 runs into hxg4 and simply loses a piece for a pawn.

That is the shape of nearly every prophylactic move you will ever play. It costs one tempo. It buys the permanent removal of one enemy idea. The trade is good when the idea was going to be annoying and bad when it was not, and that judgement is the whole skill.

The same pawn move usually does a second job, which is why it is so common: it gives the king an escape square, so the back rank stops being a mating net. See luft for that half of it.

The question, in the form a 1200 can use

Forget the word. On every move, before you decide anything, do this: pretend it is your opponent's turn and find their best move. Not their whole plan, just the one move they would most like to play. Then ask whether you can stop it, and whether stopping it costs less than allowing it.

Nine times out of ten you will find they had a threat you had not seen, and the exercise turns into a blunder-check, which is worth doing anyway. The tenth time you find a genuinely prophylactic move and it is often the best move on the board. Both outcomes are profitable, which is unusual for chess advice.

The mistake to avoid is prophylaxis as a habit. h3 and a3 played automatically, every game, against ideas your opponent was not having, are two lost moves and a slightly weakened king. Strong players disagree about specific cases like an early h3 in the Italian, and the disagreement is real, but nobody defends playing it without a reason.

What it looks like in practice

h3 or h6 to stop a bishop coming to g4 or g5 and pinning a knight.
a3 or a6 to stop a knight or bishop landing on b4 and hitting a pinned piece.
Kh1 before pushing the f-pawn, so the king is off the diagonal the push opens.
A rook to a file your opponent was about to open, arriving before they do.
Taking a piece that is not doing anything yet, because it was one move away from an outpost you cannot cover twice.

The advanced version of the same idea is restraint: not stopping one move, but making a whole plan permanently unavailable, usually by controlling the square a pawn break needs. That is the part of Nimzowitsch worth reading. The beginner version, asking what they want, wins more rating points per hour than anything else on this site.

Questions people ask

What is prophylaxis in chess in simple terms?

It is playing a move whose purpose is to stop your opponent doing something, instead of a move that improves your own position. The practical form is a question you ask before every move: if it were their turn, what would they play? If the answer is unpleasant, preventing it is often better than pressing on with your own plan.

Is h3 always a good prophylactic move?

No, and this is a genuine argument among strong players. In many quiet openings h3 usefully removes the pin on f3 for one move of time. In sharp positions it is a move you did not have, and it puts a target on the kingside for a later g-pawn or h-pawn advance. Play it when there is a bishop that actually wants g4, not out of habit.

Who invented prophylaxis in chess?

The term comes from Aron Nimzowitsch, who set it out in My System in the 1920s alongside restraint, blockade and overprotection. The moves themselves were being played long before he named them; what he added was the idea that preventing your opponent's plan is a legitimate reason for a move, worth a tempo on its own.

Prophylaxis sits under Time and plans in the reference. Nearby: