Logic grid puzzles look intimidating: a wall of clues and a grid of empty squares. But every fair puzzle is solved by the same handful of moves, repeated. Learn them once and you will never need to guess again.
We build Logic Parlor, and every puzzle in it is checked by a solver that uses only the techniques below. If the solver can’t finish a puzzle with them, the puzzle never ships. So this isn’t a list of tips. It is the complete toolkit.
How a logic grid puzzle works
You get a few categories, such as people, pets and ages, each with the same number of items. Every person has exactly one pet and exactly one age, and no two people share either. The clues narrow things down until only one arrangement fits.
The grid has a block for every pair of categories: people × pets, people × ages, and ages × pets. You mark a cell ✓ when two items belong together and ✗ when they don’t. When every row in every block has its ✓, you’re done.
The 7 techniques
1. Mark every direct clue first
Some clues simply state a fact: “Ana owns the parrot” (✓ at Ana/parrot) or “Maria doesn’t own the dog” (✗ at Maria/dog). Mark all of these before anything else. They are free progress, and every later technique feeds on marks.
2. One ✓ crosses out its whole row and column
This is the workhorse. Because each person has exactly one pet, a ✓ at Ana/parrot means Ana owns nothing else and nobody else owns the parrot. Cross out the rest of that row and column. Many apps, including Logic Parlor, can do this for you automatically.
3. The last one standing is a ✓
The same rule works in reverse. If every cell in a row is ✗ except one, that last cell must be ✓. This is how most of the grid fills in once you have a few crosses.
4. Carry marks from one grid to another
The grids are connected. If Ana owns the parrot (✓) and the parrot’s owner is 40 (✓), then Ana is 40, even though no single clue says so. And if Ana owns the parrot but the parrot’s owner is not 40, then Ana is not 40 either. Whenever you place a ✓, look at the other blocks that share its row or column and copy across what you know.
5. “Either … or” means exactly one
“The 40-year-old is either Ana or the cat’s owner” packs in three facts:
- The 40-year-old is one of those two.
- Not both, so Ana is not the cat’s owner.
- Anyone who is neither Ana nor the cat’s owner is not 40.
As soon as you rule out one option, the other is confirmed. “Of Tom and the parrot’s owner, one is 30 and the other lives in York” works the same way: learn which one is 30 and the rest falls into place.
6. Work order clues from both ends
“Ben is younger than the dog’s owner” tells you Ben is not the dog’s owner, Ben is not the oldest, and the dog’s owner is not the youngest. Exact gaps are even stronger: “The fish’s owner is exactly 10 years older than Tom”, with ages 30, 35, 40 and 45, means the fish’s owner can only be 40 or 45 and Tom can only be 30 or 35.
7. Read the hidden ✗ in group clues
“Neither Ana nor the Leeds resident owns the fish” gives two ✗ marks, plus a third: Ana is not the Leeds resident, because the clue treats them as two different people. “Ana, the cat’s owner and the 35-year-old are three different people” gives a ✗ for every pair.
Puzzles that never ask you to guess.
Every Logic Parlor puzzle is solvable with exactly these seven techniques, with big readable clues and hints that explain the next step. Free, offline, for iPhone, iPad and Android.
See Logic Parlor →A worked example
Here is Logic Parlor’s first puzzle. Four friends (Ana, Ben, Maria and Tom) each own a different pet (cat, dog, fish, parrot) and are different ages (30, 35, 40, 45).
- Ana owns the parrot.
- Ben is younger than the dog’s owner.
- The fish’s owner is exactly 10 years older than Tom.
- The 40-year-old is either Ana or the cat’s owner.
- Maria doesn’t own the dog.
Try it yourself first, then follow along:
| Step | Reasoning | Technique |
|---|---|---|
| 1 | Clue 1: Ana ✓ parrot. Cross out Ana’s other pets and everyone else’s parrot. | 1, 2 |
| 2 | Clue 2: Ben isn’t the dog’s owner, Ben isn’t 45, and the dog’s owner isn’t 30. | 6 |
| 3 | Clue 5: Maria isn’t the dog’s owner. Ana, Ben and Maria are all ✗ for the dog, so Tom owns the dog. | 1, 3 |
| 4 | Clue 3: Tom is 30 or 35. The dog’s owner isn’t 30 (step 2) and Tom owns the dog, so Tom is 35, which makes the fish’s owner 45. | 6, 4 |
| 5 | Ben isn’t 45 (step 2), so Ben doesn’t own the fish. Ben’s only pet left is the cat: Ben owns the cat and Maria owns the fish, so Maria is 45. | 4, 3 |
| 6 | Ana and Ben share 30 and 40. Ben is younger than the dog’s owner (35), so Ben is 30 and Ana is 40. | 6, 3 |
| 7 | Check clue 4: the 40-year-old is Ana, not the cat’s owner (Ben). Exactly one, as required. | 5 |
Solution: Ana, parrot, 40 · Ben, cat, 30 · Maria, fish, 45 · Tom, dog, 35. No guesses: every mark followed from a clue or from marks already on the grid.
What to do when you’re stuck
- Sweep the rows. Look for any row or column with a single empty cell left.
- Re-read comparison clues against the ages that are still possible. A clue that did nothing at the start often decides the puzzle later.
- Ask what each clue rules out, not only what it says. Most missed deductions are hidden ✗ marks.
- Check your marks. One wrong ✗ early on makes a fair puzzle look impossible. A good hint system will tell you when the board has a mistake before it tells you anything else.
That last point is how Logic Parlor’s hints work: they first check whether any mark on your board is wrong, and only then show the next deduction with the reasoning, using the techniques above. You learn the move instead of just being given the answer.