Pointing Pairs and Pointing Triples: Locked Candidates Made Simple
Pointing Pairs and Pointing Triples are locked candidate patterns within a single 3x3 box. They occur when all possible positions for a candidate digit in that box are aligned in the same row or column. This alignment allows you to eliminate that candidate from the rest of that intersecting row or column outside the box.
These are fundamental intermediate techniques that help you progress when basic methods like scanning for singles are exhausted. Understanding [Pointing Pairs](/techniques/pointing-pairs) and their three-cell counterpart is a crucial step before moving to more advanced strategies.
What Is a Pointing Pair?
A Pointing Pair is a situation where a specific candidate number appears only twice within a 3x3 box, and crucially, those two appearances are in the same row or the same column. Because the digit must be placed in one of those two cells to satisfy the box rule, it cannot appear anywhere else in that row or column outside of the box.
For example, if in a box, the candidate '5' only appears in two cells that are both in row 5, you know the '5' for that box must be placed somewhere in row 5. Therefore, you can safely remove '5' as a candidate from all other cells in row 5 that lie outside of this box.
- Focus on one candidate number at a time when scanning a box.
- Look for boxes where a candidate appears only 2 or 3 times.
What Is a Pointing Triple?
A Pointing Triple follows the exact same logic but with three cells. It occurs when a candidate number appears only three times within a box, and all three of those cells are in the same row or column. Just like with a pair, this locks the candidate's placement in that box to a specific line.
The elimination is identical: you can remove that candidate from all other cells in that row or column outside the original box. While triples are less common than pairs, they are just as valid and powerful when you spot them.
Why Is This Elimination Valid?
The validity rests on the basic rules of Sudoku. Every digit 1-9 must appear exactly once in each row, column, and 3x3 box. When all instances of a candidate within a box are confined to one row, the box's requirement for that digit forces it into that row.
Consequently, that row's requirement for the digit will be satisfied by the placement within the box. This means the digit cannot also be placed elsewhere in the same row, as that would create a duplicate. The same logic applies to a column.
How to Find Pointing Pairs and Triples
Systematic scanning is key. Focus on one 3x3 box at a time. For each candidate number (1 through 9), count how many cells in that box contain it as a possibility. If the count is two or three, check their positions.
Ask: Are all these cells in the same row? Or are they all in the same column? If the answer is yes, you have found a locked candidate pattern. Immediately look along that entire row or column, and erase the candidate from any cells outside the box you are examining.
This technique often works in tandem with others. For instance, after making an elimination with a Pointing Pairs move, you might reveal a Naked Pair in another unit, creating a cascade of logic.
Pointing Pairs vs. Claiming (Box-Line Reduction)
These two techniques are mirror images, both dealing with locked candidates. A Pointing Pair/Triple starts its logic within a box and eliminates candidates in the intersecting row or column. Its inverse is called Claiming or Box-Line Reduction.
Box-Line Reduction starts its logic within a row or column. If all candidates for a digit in a row are confined to a single box, you can eliminate that digit from the rest of the box. Both techniques use the same 'locked candidate' principle but apply it from different starting points. For a deeper dive, see our Box-Line Reduction Guide.
Key Facts
- ▪A Pointing Pair is a locked candidate pattern where two cells in a box for the same digit share a row or column.
- ▪A Pointing Triple is the same pattern but with three cells in a box aligned in one row or column.
- ▪The technique allows you to eliminate that candidate digit from the rest of the shared row or column outside the box.
- ▪The logic is valid because the box rule forces the digit into that line, satisfying the line rule there.
- ▪To find them, scan each box and look for candidates that appear only 2 or 3 times and are aligned.
- ▪Pointing Pairs/Triples and Box-Line Reduction are complementary techniques based on the same locked candidate principle.
- ▪This is considered an intermediate technique, essential for solving puzzles beyond the easy level.
- ▪Mastering this pattern often creates new opportunities to apply simpler techniques like finding Naked Singles.
Frequently Asked Questions
What is a Pointing Pair in Sudoku?
A Pointing Pair occurs when a candidate appears only twice in a 3x3 box, and both cells are in the same row or column. This lets you remove that candidate from the rest of that row/column outside the box.
What's the difference between a Pointing Triple and a Naked Triple?
A Pointing Triple involves three cells for one candidate within a single box and line, eliminating that candidate elsewhere on the line. A Naked Triple involves three cells sharing three candidates, eliminating those candidates from other cells in the same unit.
Why can I eliminate numbers with a Pointing Pair?
The digit must go in that box, and the only options are on one line. Therefore, that line's digit will be placed inside the box, so it cannot be placed elsewhere on the same line outside the box.
How is a Pointing Pair different from Box-Line Reduction?
They are mirror techniques. A Pointing Pair starts in a box and eliminates in a line. Box-Line Reduction starts in a line and eliminates in a box. Both use the 'locked candidate' concept.
Do I need to pencil mark all candidates to use this?
Yes, full candidate notation (pencil marks) is typically required to reliably spot Pointing Pairs and Triples, as you need to see all possible positions for a digit within a box.