Einstein's riddle: who owns the fish?

The German owns the fish. He lives in the green house, drinks coffee and smokes Prince. Here's the whole puzzle, the finished grid, and how to get there one clue at a time, with no guessing.

The puzzle

There are five houses in a row, each painted a different color. In each lives a person of a different nationality. Each owner drinks a different drink, smokes a different brand and keeps a different pet.

1. The Brit lives in the red house.
2. The Swede keeps dogs.
3. The Dane drinks tea.
4. The green house is immediately to the left of the white house.
5. The owner of the green house drinks coffee.
6. The person who smokes Pall Mall keeps birds.
7. The owner of the yellow house smokes Dunhill.
8. The person in the center house drinks milk.
9. The Norwegian lives in the first house.
10. The person who smokes Blends lives next to the one who keeps cats.
11. The person who keeps a horse lives next to the one who smokes Dunhill.
12. The person who smokes Bluemasters drinks beer.
13. The German smokes Prince.
14. The Norwegian lives next to the blue house.
15. The person who smokes Blends lives next to the one who drinks water.

Who owns the fish?

The answer

Houses are numbered from left to right. The fish is the only pet no clue mentions, so it's the last one left, in house 4.

The solution, step by step

1. Start with what's given. The Norwegian is in house 1 (clue 9), and house 3 drinks milk (clue 8).
2. Blue is house 2. The Norwegian lives next to the blue house (clue 14), and house 1's only neighbor is house 2.
3. Green is house 4, white is house 5. Green sits immediately left of white (clue 4), so it isn't house 5. It can't be house 2, which is blue, or house 1, because then white would be house 2. It can't be house 3, because the green house drinks coffee (clue 5) and house 3 drinks milk. That leaves green in 4 and white in 5.
4. Yellow is house 1, red is house 3, and the Brit lives there. Red and yellow are left for houses 1 and 3. The Brit lives in the red house (clue 1), and house 1 belongs to the Norwegian, so house 1 is yellow.
5. House 1 smokes Dunhill, so the horse is in house 2. The yellow house smokes Dunhill (clue 7), and the horse lives next to Dunhill (clue 11).
6. House 1 drinks water. Houses 1, 2 and 5 share tea, beer and water. The Norwegian isn't the Dane, so not tea (clue 3). Beer goes with Bluemasters (clue 12), and house 1 smokes Dunhill, so not beer.
7. House 2 smokes Blends. Blends lives next to the water drinker (clue 15), and house 1's only neighbor is house 2.
8. House 2 drinks tea and is the Dane. House 5 drinks beer and smokes Bluemasters. House 2 can't drink beer, because beer goes with Bluemasters and house 2 smokes Blends. So house 2 has tea, the Dane lives there (clue 3), and beer and Bluemasters go to house 5.
9. The German is in house 4, the Swede in house 5. They're the two owners left. The German smokes Prince (clue 13), and house 5 already smokes Bluemasters. That leaves Pall Mall for house 3.
10. Birds in house 3, dogs in house 5. Pall Mall keeps birds (clue 6). The Swede keeps dogs (clue 2).
11. Cats in house 1. Blends, in house 2, lives next to the cats (clue 10). House 3 has birds, so the cats are in house 1.
12. The fish is in house 4, with the German. It's the only pet left, and house 4 is the only house without one.

Every step there was one of a few moves: place what a clue fixes, rule out what it forbids, and look for the only option left. How to solve logic puzzles shows those moves on their own, with pictures.

Did Einstein write it?

Almost certainly not. The story that Albert Einstein wrote it as a boy, and the claim that only 2% of people can solve it, are popular but come with no evidence. It's sometimes credited to Lewis Carroll instead, also without evidence. The earliest known version appeared in Life International magazine on December 17, 1962, as "Who Owns the Zebra?". That version used different nationalities and cigarette brands, and asked who drinks water and who owns the zebra, which is why this kind of puzzle is also called a zebra puzzle.

Want the same logic, in pictures?

Hence is a daily logic puzzle built on the same reasoning as Einstein's riddle: categories in rows, clues about who sits next to whom, and one solution you reach without guessing. The clues are pictures instead of sentences, and there's a new 4x4 and 6x6 every day. Try a tiny one here.