What Is a Swordfish?
A Swordfish is a candidate elimination pattern that extends the X-Wing logic from two rows to three. You look for a specific candidate number that appears in two or three cells in each of three different rows, where all of those cells fall within the same three columns. When this pattern holds, the candidate can be eliminated from all other cells in those three columns.
The reverse also works: three columns with the candidate in two or three cells each, all falling within three rows. Then you eliminate from the rows instead.
The name "Swordfish" continues the fish metaphor from X-Wing. The next size up (four rows, four columns) is called Jellyfish.
Why Swordfish Works
The logic is the same as X-Wing, just scaled up. If a candidate can only appear in positions that fall within three columns across three rows, then those three rows will collectively "claim" one placement per column. That means no other row can place the candidate in those columns.
Think of it this way: three rows each need the candidate exactly once, and all their options are concentrated in three columns. Since three placements across three columns means one per column, every other cell in those columns can have the candidate removed.
Prerequisites
Before looking for Swordfish, you should be comfortable with these techniques:
Naked singles and hidden singles — the foundation of all solving.
Naked pairs and hidden pairs — intermediate candidate elimination.
Pointing pairs and box-line reduction — box-line interactions.
X-Wing — the 2-row version of the same logic. Understand X-Wing first.
Swordfish is an advanced technique. You will typically encounter it only in expert and evil puzzles, and only after the techniques above have been exhausted.
Step by Step: Spotting a Swordfish
Step 1: Choose a candidate number — say, 4. Make sure your pencil marks are fully updated.
Step 2: Scan each row and identify those where the candidate 4 appears in only 2 or 3 cells. Rows with 4 or more positions for the candidate cannot participate.
Step 3: From those qualifying rows, check whether any group of three shares the same three columns. The candidate does not need to appear in all three columns in every row — it just needs to appear in a subset of those three columns per row.
Step 4: If you find such a group, the elimination: remove the candidate 4 from all other cells in those three columns that are not in the three Swordfish rows.
Worked Example
Suppose you are tracking the candidate 6 across the grid. You notice:
In Row 1, the candidate 6 appears only in Column 2 and Column 7.
In Row 4, the candidate 6 appears in Column 2, Column 5, and Column 7.
In Row 8, the candidate 6 appears only in Column 5 and Column 7.
All positions fall within Columns 2, 5, and 7 — three columns. This is a Swordfish.
The three rows will place the number 6 exactly once each, and all placements are confined to Columns 2, 5, and 7. One column gets one placement each. So you can eliminate the candidate 6 from every other cell in Columns 2, 5, and 7 — any cell that is not in Row 1, Row 4, or Row 8.
For instance, if Row 6 Column 5 also had 6 as a candidate, you would remove it. That elimination might reveal a naked single or enable another technique.
Spotting Checklist
1. Pick a candidate number.
2. Find rows where that candidate appears in only 2 or 3 cells.
3. Can you select 3 such rows where all candidate positions fall within the same 3 columns?
4. If yes: eliminate the candidate from other cells in those 3 columns.
Validation: Is This Really a Swordfish?
Check 1: You have exactly 3 rows involved. Two rows would be an X-Wing. Four would be a Jellyfish.
Check 2: Each row has the candidate in at most 3 positions, and all positions fall within the same 3 columns.
Check 3: The elimination only removes candidates from other cells in the 3 columns — never from the Swordfish cells themselves.
Common Mistakes
Confusing Swordfish with X-Wing. If only two rows are involved, it is an X-Wing, not a Swordfish. Count your rows carefully.
Rows with too many positions. If a row has the candidate in four or more cells, it cannot be part of a Swordfish. The positions would spill outside the three-column constraint.
Columns do not align. All candidate positions across the three rows must fit within exactly three columns. If they span four columns, the pattern breaks.
Stale pencil marks. Swordfish depends on accurate candidate tracking. A single missing or extra pencil mark can hide a valid pattern or create a false one. Update your pencil marks after every placement.
Trying Swordfish too early. If you have not exhausted singles, pairs, pointing pairs, box-line reduction, and X-Wing, you are looking in the wrong place. Swordfish is a last-resort technique for expert-level puzzles.
Swordfish vs. X-Wing vs. Jellyfish
These three techniques use the same logic at different scales:
X-Wing: 2 rows, 2 columns. The most common fish pattern. Appears in most hard puzzles.
Swordfish: 3 rows, 3 columns. Less common. Typically needed only in expert and evil puzzles.
Jellyfish: 4 rows, 4 columns. Extremely rare. Most solvers never encounter one in practice.
If you understand the logic behind X-Wing, you already understand Swordfish and Jellyfish — the only difference is how many rows and columns are involved.
Frequently Asked Questions
What is the difference between Swordfish and X-Wing?
X-Wing uses 2 rows and 2 columns. Swordfish extends the same logic to 3 rows and 3 columns. The pattern is larger but the elimination principle is identical.
How common is Swordfish?
Swordfish is rare in medium puzzles but appears regularly in expert and evil puzzles. Most hard puzzles can be solved without it.
Do I need to learn X-Wing before Swordfish?
Yes. X-Wing is the simpler 2-row version of the same logic. Understanding X-Wing first makes Swordfish much easier to grasp.
Can Swordfish have fewer than 6 cells?
Yes. A Swordfish requires a candidate in at most 3 positions per row, but some rows may have only 2. The minimum is 6 cells (2 per row), the maximum is 9 (3 per row). The key requirement is that all positions fall within the same 3 columns.