Odd and Even Threats in Four in a Row

This is the advanced Connect 4 strategy that strong players and computers use. It explains why some threats win and others never get used.

Number the rows

Count the rows from the bottom: row 1 is the bottom and row 6 is the top. Rows 1, 3 and 5 are odd; rows 2, 4 and 6 are even.

Why row numbers matter

Near the end of a game, players often have to fill up columns one disc at a time. When the board fills evenly, the first player tends to fill the odd-row spaces and the second player the even-row spaces. So:

• If you went first, threats on odd rows (3 and 5) are strong. Your opponent will eventually be forced to play below them, giving you the win.
• If you went second, threats on even rows (2, 4 and 6) are strong for the same reason.

A threat on the “wrong” row type for you is far less likely to be used.

Zugzwang

Zugzwang is a German chess word for a position where every move makes things worse. In Four in a Row, it means your opponent has to play a disc, and every column they can choose lets you win. Good odd and even threats create zugzwang.

Putting it into practice

1. Note whether you went first or second.
2. When building threats, prefer rows of your type.
3. Don’t waste moves on threats your opponent will never have to give you.
4. Late in the game, count the empty spaces column by column to see who will be forced to play where.

Test yourself against the Hard computer.