Hempel's Paradox: Can You Prove That All Strawberries Are Red Using A Green-Eyed Person?


Philosophy is full of mind blowing paradoxes, but some are particularly interesting. Raven paradox, also known as the Hempel’s paradox, is one of them. Let’s see what it’s about.

This paradox was first proposed by the logician Carl Gustav Hempel in the 1940s.


His purpose was to illustrate a contradiction between inductive logic and intuition.

In the original version of the paradox, Hempel uses ravens as examples.


These two are the premises of the original argument:

1. All ravens are black.
2. Everything that is not black is not a raven.

In strict logical terms, via contraposition, these statements are equivalent to each other.


Now let’s adapt this logic of thinking to our own example.

  • All strawberries are red.

  • Everything that is not red is not a strawberry.

Accordingly, if the first sentence is correct, the second sentence is automatically correct because there is no non-red strawberries.

In addition to this, if the second sentence is true, the first sentence will also be true, since no strawberry exists in any color other than red.

It seems that there are two things that need to be done to prove these two arguments.


For the first argument, we need to observe that all the strawberries are red, and for the second argument, we have to examine all the non-red materials to show that there are not even one strawberry among them.

The paradox arises when we go into detail.


Let's first think of a red strawberry. This strawberry is a proof that all strawberries are red, which was suggested by the first argument.

Now, let's think of a green-eyed person as a second example, just to stir things up a bit.

This person is not a strawberry, and their eyes are not red. Therefore, we’ve obtained evidence supporting the expression, “Everything that is not red is not a strawberry”.

Remember that those two statements were equivalent to each other.

Therefore, the evidence supporting the second argument also supports the original argument, which is, all strawberries are red.

So the existence of a green-eyed person can be shown as evidence that all strawberries are red according to the paradox.

There are some philosophers criticizing Hempel’s paradox arguing that it damages the reputation of inductive logic.

However, since it kind of recommends us to avoid mere generalizations, it’s a good paradox that might be helpful especially for scientists.

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