Transposition (chess)

In chess, a transposition is a sequence of moves that results in a position that may also be reached by another, more common sequence of moves. Transpositions are particularly common in the opening, where a given position may be reached by different sequences of moves. Players sometimes use transpositions deliberately, to avoid variations they dislike, lure opponents into unfamiliar or uncomfortable territory or simply to worry opponents. To transpose is to play a move that results in a transposition.

Transposition tables are an essential part of a computer chess program.

Transpositions exist in other abstract strategy games such as shogi, Go, tic-tac-toe and Hex.

Examples

Positions reached by different routes

	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

Position can arise from Queen's Gambit or English Opening.

For instance, the first position can be obtained from the Queen's Gambit:

1. d4 d5

2. c4 e6

3. Nc3 Nf6

But this position can also be reached from the English Opening:

1. c4 e6

2. Nc3 Nf6

3. d4 d5

so the English Opening has transposed into the Queen's Gambit.

	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

Position can arise from French Defense or Petrov Defense.

The second position shows another example. The position can arise from the French Defence:

1. e4 e6

2. d4 d5

3. exd5 exd5

4. Nf3 Nf6

The identical position can also be reached, with two extra moves played by each side, from the Petrov Defense:

1. e4 e5

2. Nf3 Nf6

3. Nxe5 d6

4. Nf3 Nxe4

5. d3 Nf6

6. d4 d5

	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

Position can arise from Queen's Gambit Declined or Nimzo-Indian Defence.

This third position shows another example. This position can be reached from the Exchange variation of the Queen's Gambit Declined:

1. d4 d5

2. c4 e6

3. Nc3 Nf6

4. cxd5 exd5

5. Bg5 Bb4

6. Qc2 h6

The identical position can also be reached from the Classical variation of the Nimzo-Indian Defence:

1. d4 Nf6

2. c4 e6

3. Nc3 Bb4

4. Qc2 d5

5. cxd5 exd5

6. Bg5 h6

Transposition possibilities of some openings

Some openings are noted for their wide range of possible transpositions, for example the Catalan Opening and Sicilian Defence.

For a simple example, the opening moves 1.d4 e6 (the Horwitz Defence) can transpose very quickly into a wide range of openings, including:

	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

Queen's Gambit Declined, after 2.c4 d5. The QGD itself offers a wide range of transpositional possibilities.

	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

After 2.c4 Nf6. This could develop in many ways, including: Queen's Gambit Declined, Nimzo-Indian Defense, Queen's Indian Defense or Modern Benoni Defense.

	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

Dutch Defense, after 2.c4 f5

	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

English Defense, after 2.c4 b6

	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

French Defence, after 2.e4 d5

	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

Franco-Benoni, after 2.e4 c5. This can transpose into various types of Benoni Defense after 3.d5, into the Alapin Variation of the Sicilian Defense after 3.c3, or into main lines of the Sicilian Defense after 3.Nf3 cxd4 4.Nxd4.