May 27, 2024


Science It Works

Did you solve it? Logical philosophers | Logic puzzles

Earlier today I set you the following three puzzles.

1. Late Wittgenstein

Wittgenstein has been murdered. The culprit is one of either Friedrich Nietzsche, Lou Andreas-Salomé, Karl Marx or Ludwig Feuerbach. They make the following statements. You have been correctly informed that guilty person always lies, and everyone else tells the truth.

Nietzsche: Salomé is the culprit.
Salomé: Marx is innocent.
Feuerbach: Salomé’s statement is true.
Marx: Nietzsche’s statement is false.

Who killed Wittgenstein?

Solution: Nietzsche.

If Nietzsche is telling the truth, then Salomé is the culprit and therefore a liar. Thus Marx is not innocent, meaning he is the culprit. We can’t have two culprits, since this is forbidden in the setting of the question, and so we are led to contradiction. Nietzsche must therefore be lying. If he is lying, then everyone else tells the truth, which they can without contradiction. Thus Nietzsche killed Wittgenstein.

2. An existential problem

Sun Tzu, Iris Murdoch and Aristotle are each offering you a lift. Two of them want to kill you. One doesn’t want to kill you. You must choose to leave with the philosopher who does not want to kill you.

You are told (correctly) that at least one of the philosophers will always lie to you (this may or may not be one of the ones that wants to kill you.)

They make the following statements:

Sun Tzu: Murdoch and Aristotle speak the truth.
Murdoch: To survive, choose Sun Tzu, or choose Aristotle
Aristotle: Murdoch is NOT the one to choose if you want to live.

Which philosopher do you choose?

Solution Murdoch

If Sun Tzu speaks the truth, then Murdoch and Aristotle also speak the truth. We know that at least one of them is lying, so we conclude that Sun Tzu must be lying. We thus have three possible situations. Either Murdoch and Aristotle are both liars (in which case Murdoch is the one to choose), or Murdoch is a liar and Aristotle tells the truth, in which case there is a contradiction, or Murdoch tells the truth and Aristotle is a liar, in which case there is also a contradiction.

The only logical conclusion is to go with Murdoch.

3. The Café de Flore

The French philosophers Raymond Aron, Simone de Beauvoir, Albert Camus, Maurice Merleau-Ponty and Jean Paul Sartre were drinking in the famous Parisian watering hole. Four of them were sitting at one table, and one was on their own at the other side of the room. They were all drinking different drinks.

1. The one who drank beer sat next to Sartre, who never drank gin.
2. de Beauvoir sat adjacent to the one who drank the apricot cocktail, who was not Sartre.
3. Camus, who never drank wine, did not sit near the one who drank the beer.
4. The one who drank the G&T and the one who drank the beer, and Merleau-Ponty drank neither, were sitting next to each other.
5. Merleau-Ponty did not drink whisky or wine.

Who is drinking which drink, and which one is drinking alone?

Solution: Aron/beer, de Beauvoir/G&T, Camus/whisky, Merleau-Ponty/apricot cocktail, Sartre/wine. Camus is drinking alone.

The easiest way to do this puzzle is to draw up a 5 x 5 grid, with the names of the philosophers down one side, and the drinks – beer, G&T, apricot cocktail, whisky and wine – across the top. Fill in the grid, placing an X wherever you know that the philosopher in that row was not drinking the drink in that column.

From 5, place crosses in the cells where Merleau-Ponty meets whisky and wine. From four, eliminate Merleau-Ponty with G&T and beer. We can place a tick on Merleau-Ponty and apricot cocktail, and place an X in every other cell in the apricot cocktail column. I will leave you to fill in the rest!

From 1 and 3 we deduce that Camus must be the philosopher sitting alone.

Thanks again to Jonny Thomson for the puzzles. Jonny is the author of the splendid new book Mini Philosophy, which has 150 mini essays about great thinkers and the thoughts they thunk.

I set a puzzle here every two weeks on a Monday. I’m always on the look-out for great puzzles. If you would like to suggest one, email me.

I’m the author of several books of puzzles, most recently the Language Lover’s Puzzle Book. I also give school talks about maths and puzzles (restrictions allowing). If your school is interested please get in touch.