Introduction

The Obvious Pairs technique is a fundamental Sudoku solving method that helps eliminate impossible candidates and reveal new placements. Like Obvious Singles, this technique relies on proper notes placement to identify patterns that aren't immediately visible.

Understanding Obvious Pairs is essential for progressing from easy to medium difficulty puzzles. This technique works by recognizing when two cells in a 3×3 block share the same pair of candidates, which means those two numbers must go in those two cells, allowing you to eliminate them from other cells in the block.

What Is the Obvious Pairs Technique?

The Obvious Pairs technique is a Sudoku solving method based on correct notes placement. It applies when you find two cells within the same 3×3 block that contain exactly the same pair of notes (candidates). When two cells share the same two candidates, those numbers must go in those two cells—one number in each cell, though you may not know which goes where yet.

Since these two numbers must occupy these two cells, they cannot appear in any other cells within that 3×3 block. This allows you to remove these candidates from all other cells' notes in the block, which often reveals new Obvious Singles or creates other solving opportunities.

Obvious Pairs is also known as Naked Pairs, and it's one of the first intermediate techniques players learn after mastering basic single candidate methods. It's particularly effective in medium difficulty puzzles where notes become essential for progress.

Key Points

Understanding these fundamentals helps you master Obvious Pairs:

Requires notes: Obvious Pairs can only be identified when you have proper notes (pencil marks) showing all possible candidates
Two cells, two candidates: The technique applies when exactly two cells in a block share exactly the same two candidates
Elimination opportunity: The pair's candidates can be removed from all other cells in the same 3×3 block
Works in blocks first: While pairs can occur in rows and columns, this technique focuses on 3×3 blocks
Creates chain reactions: After elimination, new Obvious Singles often appear, leading to more placements
Foundation technique: Mastering Obvious Pairs prepares you for more advanced techniques like Obvious Triples

How It Works (Step-by-Step)

Follow these steps to identify and apply the Obvious Pairs technique:

Step 1: Enable Notes or Pencil Marks

Start by enabling notes mode on your Sudoku grid. Fill in all possible candidates for each empty cell based on what numbers are already present in that cell's row, column, and box. Obvious Pairs cannot be identified without visible notes showing all candidates.

Step 2: Scan Each 3×3 Block Systematically

Work through each of the nine 3×3 blocks one at a time. Look for cells that have exactly two candidates in their notes. These are potential members of an Obvious Pair.

Step 3: Look for Matching Pairs

Within each block, check if any two cells share exactly the same two candidates. For example, if one cell has candidates 7 and 9, and another cell in the same block also has candidates 7 and 9, you've found an Obvious Pair.

Step 4: Verify the Pair

Confirm that the two cells are in the same 3×3 block and that they share exactly the same two candidates—no more, no less. If one cell has 7, 9, and another candidate, or if the cells are in different blocks, this technique doesn't apply.

Step 5: Eliminate Candidates from Other Cells

Since the two numbers in the pair must go in those two cells, remove those candidates from all other cells' notes within the same 3×3 block. This elimination is the key benefit of identifying Obvious Pairs.

Step 6: Update Your Notes

After eliminating candidates, update your notes throughout the block. Removing candidates may reveal new Obvious Singles—cells that now have only one candidate remaining.

Step 7: Apply Obvious Singles

After eliminating candidates from the Obvious Pair, scan the block for cells with only one candidate remaining. These are Obvious Singles that you can place immediately. Continue this process as each placement may create new opportunities.

Examples

Here are practical examples demonstrating how Obvious Pairs works:

Example 1: Basic Obvious Pair in a Block

You're examining a 3×3 block with several empty cells filled with notes. Among them, you notice two cells that both contain candidates 7 and 9. This means one of these cells must contain 7 and the other must contain 9 (though you don't know which is which yet).

Since 7 and 9 must go in these two cells, they cannot appear in any other cells within this block. You remove 7 and 9 from all other cells' notes in the block. After this elimination, you notice that one cell now has only candidate 6 remaining, and another cell has only candidate 4 remaining. These are Obvious Singles, so you place 6 and 4 in their respective cells.

Example 2: Obvious Pair Revealing Multiple Singles

In another block, you find two cells sharing candidates 3 and 5. You eliminate 3 and 5 from all other cells in the block. This elimination reveals that three other cells now have only one candidate each: one has only 2, another has only 8, and a third has only 1. You place all three numbers, making significant progress in the puzzle.

Example 3: Obvious Pair Not Applicable

You're looking at a block where one cell has candidates 4 and 6, and another cell has candidates 4, 6, and 8. This is not an Obvious Pair because the cells don't share exactly the same candidates—one has an extra candidate. The technique requires exactly the same two candidates in both cells.

Example 4: Chain Reaction After Elimination

You identify an Obvious Pair of 2 and 7 in a block and eliminate these candidates from other cells. One cell that previously had candidates 1, 2, 7, 9 now has only 1 and 9. This doesn't create an immediate single, but it reduces the cell's possibilities. Later, after other eliminations, this cell becomes a single candidate, demonstrating how Obvious Pairs set up future placements.

Example 5: Multiple Pairs in Different Blocks

You scan multiple blocks and find Obvious Pairs in three different blocks: one has a pair of 1 and 8, another has a pair of 3 and 9, and a third has a pair of 2 and 5. You eliminate candidates from each block accordingly. This systematic approach helps you make progress across the entire puzzle, not just in one area.

How Obvious Pairs Relates to Other Techniques

Obvious Pairs is part of a family of related techniques:

Obvious Singles

Obvious Singles (Naked Singles) occur when a cell has only one candidate remaining. Obvious Pairs often creates Obvious Singles after eliminating candidates. Both techniques rely on proper notes placement and work together to solve puzzles systematically.

Obvious Triples

Obvious Triples is the extension of Obvious Pairs, where three cells in a unit share the same three candidates. Understanding Obvious Pairs prepares you for learning Obvious Triples, which uses the same logic but with three cells instead of two.

Hidden Pairs

Hidden Pairs is the opposite pattern, where two candidates appear in only two cells of a unit, but those cells may have other candidates as well. Understanding both Obvious and Hidden Pairs gives you multiple ways to identify elimination opportunities.

When to Use Obvious Pairs

Obvious Pairs is most effective when:

Notes are complete: You've filled in notes for all empty cells in the block
Basic techniques are exhausted: Single candidates and last remaining cell techniques no longer reveal placements
Medium difficulty puzzles: This technique becomes essential when progressing from easy to medium puzzles
Multiple candidates visible: When cells have 2-4 candidates, Obvious Pairs become more likely to appear

Common Mistakes to Avoid

Avoid these errors when using Obvious Pairs:

Not checking for exact matches: Both cells must have exactly the same two candidates—no more, no less
Mixing units: The two cells must be in the same 3×3 block (or row/column if applying the technique there)
Forgetting to eliminate: After identifying a pair, always remove those candidates from other cells in the unit
Not updating notes: After elimination, update your notes to see new opportunities
Overlooking resulting singles: After elimination, always check for new Obvious Singles that may have appeared

Tips for Finding Obvious Pairs

These tips help you identify Obvious Pairs more efficiently:

Scan systematically: Check each block methodically rather than randomly
Look for two-candidate cells first: Cells with exactly two candidates are potential pair members
Compare candidates visually: When notes are visible, matching pairs often stand out
Work block by block: Complete one block before moving to the next
Update as you go: After each elimination, update notes immediately to see new patterns

Summary

The Obvious Pairs technique is a fundamental Sudoku solving method that helps eliminate impossible candidates and reveal new placements. By recognizing when two cells in a 3×3 block share exactly the same two candidates, you can eliminate those candidates from all other cells in the block, often creating Obvious Singles and making significant progress.

This technique requires proper notes placement and works best in medium difficulty puzzles where basic techniques are insufficient. Mastering Obvious Pairs prepares you for more advanced techniques like Obvious Triples and Hidden Pairs, building a strong foundation for intermediate and advanced solving.

Remember that Obvious Pairs works together with Obvious Singles—after eliminating candidates from a pair, always scan for new singles that may have appeared. This systematic approach of identifying pairs, eliminating candidates, and finding singles creates an effective solving cycle that helps you complete puzzles efficiently.

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❓ FAQ

Q1: What's the difference between Obvious Pairs and Naked Pairs?

They're the same technique—different names for the same method. Both refer to when two cells in a unit share exactly the same two candidates, allowing elimination of those candidates from other cells in that unit.

Q2: Do Obvious Pairs only work in 3×3 blocks?

No. While this guide focuses on blocks, Obvious Pairs can occur in rows and columns as well. The same logic applies: if two cells in a row or column share the same two candidates, those candidates can be eliminated from other cells in that row or column.

Q3: What if the two cells have more than two candidates each?

If either cell has more than two candidates, it's not an Obvious Pair. The technique requires exactly two cells with exactly the same two candidates. If cells have additional candidates, you may have a Hidden Pair instead, which is a different technique.

Q4: How do I know when to look for Obvious Pairs?

Look for Obvious Pairs when you've filled in notes for all empty cells and basic techniques like single candidates no longer reveal placements. In medium difficulty puzzles, Obvious Pairs become essential for making progress.

Q5: Can Obvious Pairs appear in rows or columns too?

Yes. While this guide emphasizes 3×3 blocks, Obvious Pairs work in any unit: rows, columns, or blocks. The same principle applies: two cells sharing the same two candidates allow elimination from other cells in that unit.

Q6: What happens after I eliminate candidates from an Obvious Pair?

After eliminating the pair's candidates from other cells, update your notes. You'll often find that some cells now have only one candidate remaining—these are Obvious Singles that you can place immediately. This chain reaction is one of the technique's main benefits.

Q7: How is Obvious Pairs different from Hidden Pairs?

Obvious Pairs occur when two cells have exactly the same two candidates (and no others). Hidden Pairs occur when two candidates appear in only two cells of a unit, but those cells may have other candidates as well. Both eliminate candidates, but they're identified differently.

Q8: Should I fill in all notes before looking for Obvious Pairs?

Yes, for best results. Obvious Pairs can only be identified when you can see all candidates in cells. If notes are incomplete, you might miss pairs or incorrectly identify them. Complete notes give you the full picture needed to spot this pattern accurately.

Obvious Pairs Technique in Sudoku: Complete Guide with Notes Strategy