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Ponderchess / Glossary

Prophylaxis in chess

Prophylaxis is a move or plan that stops the opponent's idea before it happens. Instead of only asking what you want to do, you ask what your opponent wants and take that option away, often with a quiet move such as h3 or a rook move.

White to move in the main line of the Closed Ruy Lopez. White wants to play d4, but at once Black could answer ...Bg4, pinning the f3-knight and adding pressure on d4. h3 takes the g4-square away from Black's bishop and knight first, so that d4 can follow under better conditions.9.h3

The question behind prophylaxis

Before choosing a move, ask what your opponent would play if it were their turn. If the answer is a strong move, such as a pin, a pawn break or a knight jump to a good square, consider preventing it first. A move that stops the opponent's best idea can be more valuable than one that pushes your own plan forward.

The idea was set out by Aron Nimzowitsch, and players such as Tigran Petrosian and Anatoly Karpov were known for it. Their games are full of small moves that seem to do little, after which the opponent has nothing useful to do.

Typical prophylactic moves

Many prophylactic moves are pawn moves that take a square away. In the Closed Ruy Lopez, h3 stops ...Bg4 and ...Ng4. A move such as a3 prevents ...Bb4 or ...Nb4, and a4 can stop ...b5 before it happens.

Others are piece moves. A king steps from g1 to h1 to leave the dangerous g1-a7 diagonal, a rook takes up position on a file the opponent wants to open, or a knight goes back to defend a square before the opponent can use it.

Prophylaxis versus passivity

Good prophylaxis is not timid defence. The best prophylactic moves also improve your position, so you lose nothing if the threat never comes. A move that stops an idea the opponent was not going to play, or that creates a new weakness, is just a wasted tempo.

Overprotection is a related idea: defending an important square or pawn more times than is strictly needed, so that the pieces doing it are well placed and the opponent's play against that point never gets started.

Common mistakes

  • Spending moves on prophylaxis against ideas that are not real threats, while the opponent develops freely.
  • Choosing a prophylactic move that creates a new weakness, such as a pawn move that gives up a key square.
  • Thinking only about your own plan and never asking what the opponent wants to do.

Questions about prophylaxis

What is prophylaxis in chess?

Play aimed at preventing the opponent's plans rather than pursuing your own. The term comes from medicine, where it means preventive treatment.

Why is h3 played so often?

It stops an enemy bishop or knight from using g4, removing pins and attacks on the f3-knight, and it also gives the castled king an escape square.

Is prophylaxis the same as defence?

Not quite. Defence answers a threat that already exists; prophylaxis stops the threat before it appears.

Practise it