Difficulty
Hard
Sudoku technique guide
Naked Quad
When the easy moves slow down, one clear pattern can make the next step feel possible again. Naked Quad helps you spot what the grid is already telling you.
By the end, you will know what to notice, how the idea works and when it is worth using.
At a glance
Technique family
Naked subsets
Purpose
Removes candidates
Typical puzzle stage
Middle to late
Frequency
Rare
Prerequisites
Naked Triples and confident candidate scanning
Why this technique matters
Naked Quads complete the naked-subset family. Knowing the pattern helps, but knowing when to stop looking for it saves time.
The idea in plain English
A Naked Quad is four cells in one unit whose combined candidates are exactly four digits. Those four digits are reserved for those four cells.
How to recognise it
It is usually easiest to see after other eliminations leave several compact candidate lists. Mark the four digits, then count the cells using only them.
Pause when you see this shape. You do not have to force it; just check whether the pattern is complete.
How the logic unfolds
Think of this as a short conversation with the grid. Take one check at a time, and let each answer tell you what to inspect next.
Start by. Work in one row, column or box.
Then. Find four cells with candidate lists drawn from the same four digits.
Next. Verify their combined set has no fifth digit.
Finally. Remove those four digits from other cells in the same unit.
When it usually appears
Use it only after simpler singles, locked candidates, pairs and triples have been checked.
Common traps
These are easy places to get turned around. They are useful checks, not signs that you are doing badly.
- Mistaking four cells with five combined candidates for a quad.
- Removing candidates before checking whether one of the four digits appears in an unchosen cell that changes the pattern.
Frequently asked questions
Are Naked Quads common?
No. They are useful to recognise, but simpler techniques should be your normal workflow.
Does a quad always lead to a placement?
No. It removes candidates, which may create a later placement.
Quick takeaway
- A Naked Quad belongs to the naked subsets family.
- Its purpose is to remove candidates.
- Look for a complete pattern, not one that only nearly fits.
- It is most useful middle to late.
- Once you make the deduction, return to the simpler scans.