What does Magritte mean when he says "This is not a pipe"? It sure looks like a pipe. But step back for a moment: what is the definition of the thing you are looking at? The thing you are looking at is not a pipe. The thing you are looking at is a picture. ... You see, if it were actually a pipe, you could stuff tobacco in it, smoke it, etc. But you cannot do anything like that with it. This is not a pipe. It's a picture.

We generally figure this out when we're growing up. You have a Teddy Bear. When you're a child, perhaps you very adorably treat Rupert as if he were "Bear: Subtype Stuffed". But that isn't really true! Rupert is not any kind of a bear at all, and has no actual connection to Ursus. In reality, the amusing childhood mistake is an inversion of the true state of affairs... Rupert is really a "Stuffed Toy: Subtype Bear".

Likewise, Magritte's treacherous pipe is not a "Pipe: Subtype Picture". Rather, it is a "Picture: Subtype Pipe".

Here's another fine example: consider trips to Rome. You can have an expensive trip to Rome, a long trip to Rome, a pious trip to Rome, etc. Some trips to Rome can be several of these at once. There are all sorts of trips to Rome: religious trips, business trips, sightseeing trips, etc. But what about "imaginary" trips to Rome. You don't need a passport for those, do you? That's because an imaginary trip to Rome is not a kind of a trip to Rome! It's a kind of flight of fancy, one about Rome as opposed to being about something else.

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