Five classic types of logic puzzles for adults are grid logic puzzles, sudoku, nonograms, number sequences and logic riddles. Each one asks you to reach a single answer by reasoning, not luck. Below is a worked example of each, the solving moves that matter most, and a simple plan for a short daily puzzle habit.
A logic puzzle is built on deduction. You start with a few facts or clues and work out what must be true. Lewis Carroll, the author of Alice in Wonderland, published logic problems in The Game of Logic in 1886. Today the family includes word puzzles as well as grid puzzles like sudoku and nonograms.
A good logic puzzle has three traits:
One answer. A well-made sudoku, for example, has a single solution.
No outside knowledge. Everything you need is in the clues.
Reasoning over luck. Each step can be worked out from the last, though very hard puzzles sometimes push solvers to test a guess and look for a contradiction.
A grid logic puzzle gives you a short story, a few categories and a set of clues. You mark a grid to track what is still possible. The best-known example is the Zebra Puzzle, which asks who owns the zebra.
Worked example. Ana, Ben and Cal each own one pet: a cat, a dog or a fish. Clue 1: Ana is allergic to fur. Clue 2: Ben does not own the dog.
Draw a 3 by 3 grid with names down the side and pets across the top.
Clue 1 rules out the cat and the dog for Ana. Mark an X in both boxes. Only the fish is left, so give Ana the fish with a check.
Each pet has one owner, so cross out the fish for Ben and Cal.
Clue 2 rules out the dog for Ben. With the fish gone too, Ben owns the cat.
Cal owns the dog, the only pet left.
Tip: Every time you place a check, cross out the rest of that row and column. Forgetting this step is the easiest way to get stuck.
Classic sudoku is a 9 by 9 grid split into nine 3 by 3 boxes. You fill it so every row, column and box holds the digits 1 to 9 exactly once. The modern form first ran in 1979 in Dell Magazines as Number Place. The name sudoku came from the Japanese publisher Nikoli, and the puzzle became a newspaper staple in Britain from 2004.
Worked example: find the only square left. Say the top-left box still needs a 7. The first row already has a 7 in another box, and so does the second row. So this box's 7 must go in its third row. That row has two empty squares. One of them sits in a column that already has a 7 lower down the grid. That leaves exactly one square for the 7, so write it in.
Scan one digit at a time across the whole grid, starting with digits that already appear often.
Use small pencil marks for the possible digits in tricky squares.
Before you guess, look for a row, column or box with only one or two empty squares.
Nonograms, also sold as Hanjie, Picross or Griddlers, are picture puzzles. The numbers beside each row and above each column give the runs of filled squares, in order. Runs are separated by at least one blank square. Fill in every row correctly and a picture appears. They were invented in Japan in the late 1980s.
Worked example 1. A row of 5 squares has the clue 3 1. Add the runs plus one gap between them: 3 + 1 + 1 = 5. That fills the row exactly, so it reads filled, filled, filled, blank, filled.
Worked example 2: the overlap trick. A row of 10 squares has the clue 8. The run could start in square 1, 2 or 3. However you slide it, squares 3 to 8 are always covered, so you can fill those six right away.
Tip: Mark squares you know are blank with a dot. Blanks are information too.
Sequence puzzles show a list of numbers and ask what comes next. The rule is usually hidden in the gaps.
Worked example. What comes next: 2, 6, 12, 20, 30?
Write the differences between neighbors: 4, 6, 8, 10.
The differences grow by 2 each time, so the next one is 12.
30 + 12 = 42.
Check it another way. The numbers are 1 x 2, 2 x 3, 3 x 4, 4 x 5 and 5 x 6, so the next is 6 x 7 = 42. When two methods agree, you can trust the answer.
Tip: Try differences first, then ratios (does each number double?), then squares and alternating patterns.
Logic riddles are word puzzles that reward careful reading. A classic family is knights and knaves, made popular by the logician Raymond Smullyan. Knights always tell the truth and knaves always lie.
Worked example. On an island you meet A and B. A says, "We are both knaves." What are they?
Suppose A is a knight. Then the statement is true, which would make A a knave. That is impossible.
So A is a knave, and the statement is false.
"We are both knaves" is false, so at least one of them is a knight. A is not, so B is the knight.
Tip: Test each possibility and look for a contradiction. If one case breaks the rules, the other must be true.
Anchor it. Attach your puzzle to something you already do every day, like your first coffee or the ride home.
Keep it short. Ten minutes is plenty. Stop while it is still fun so you want to come back tomorrow.
Rotate types. Try grid logic on Monday, sudoku on Tuesday, a nonogram on Wednesday, sequences on Thursday and a riddle on Friday.
Start easy. Begin a level below where you think you are. Early wins help the routine stick.
Go untimed first. Learn the solving moves before you race a clock.
Review your misses. When you get stuck, check the answer and find the step you missed. That step is the lesson.
Count days, not streaks. Aim for four or five puzzle days a week. A missed day is not a failure.
Keep your expectations honest. Practice makes you better at the puzzles you play. Whether that carries over to everyday thinking is a separate question, and our guide Do brain games work? looks at the research. Puzzles are worth doing simply because they are satisfying.
Small grid logic puzzles and mini sudoku (4 by 4 or 6 by 6) are good places to start. They use the same moves as bigger puzzles with fewer squares to track.
Turn each clue into X marks or checks on the grid. Whenever you place a check, cross out the rest of its row and column. Then reread the clues, because new marks often unlock old clues.
No. In sudoku the digits are just symbols, and you never add them. Nonograms only need counting, and most sequence puzzles use simple arithmetic.
There is no official number. Ten to fifteen minutes fits into most days and is long enough to finish a small puzzle or two. Pick a length you can keep up.
Cognilo: Brain Training Games is an iPhone and iPad app with a daily session of five short puzzles that takes about six minutes, drawn from eight puzzle types across memory, logic, numbers, spatial reasoning, focus and language. You can play untimed, timed or unrated, get a strategy tip after each round and replay any round you missed with the correct answer, and its habit tracking counts active days per week instead of demanding a daily streak. It is free to download with optional Pro subscriptions, needs no account, and has no ads or tracking.
Get Cognilo free on the App Store