Conjugate Pair

A Conjugate Pair is a pair of cells in a unit that contain a candidate and that pair of cells are the only two cells in that unit that can contain the candidate.

A Conjugate Pair has the following properties. If cell one contains the candidate then cell two cannot contain the candidate and vice-versa. Additionally, if cell one does not contain the candidate then cell two has to contain the candidate and vice-versa.

This type of link or bond between two cells is known as a Strong Link or a link with Strong Inference.In the example in Figure 1 the two blue cells in box 3 are the only two cells in box 3 that contain the candidate 1. These two cells are a conjugate pair for the value 1. They are also the only two cells in row 2 that contain the candidate 1.

The two green cells in column 3 are the only cells in column 3 to contain the value 5. These two cells are a conjugate pair for the value 5.

The two yellow cells in row 7 are the only cells in row 7 to contain the value 8. These two cells are a conjugate pair for the value 8.

There are other conjugate pairs in figure 1. See if you can spot them.

Using solving techniques that involve chains often produces results in puzzles that have multiple conjugate pairs.