It seems to be a constant throughout history: In every period, people believed things that were just ridiculous, and believed them so strongly that you would have gotten in terrible trouble for saying otherwise.

Is our time any different? To anyone who has read any amount of history, the answer is almost certainly no. It would be a remarkable coincidence if ours were the first era to get everything just right.

How can we find a general recipe for discovering things that are true that you can’t say?

• The Conformist Test: People seem to think that there is something wrong with you if you think things you don’t dare say out loud. This seems backward. Almost certainly, there is something wrong with you if you don't think things you don't dare say out loud.
• Trouble: If you say that 2+2=5, people won’t get angry at you. They’ll either think that you’re joking, or that you’re insane. The things that people get angry at are the ones that they worry might be true.
• Heresy: Trouble obviously doesn’t get us all the answers. What about the things so controversial that no one even talks about them? How do we find these? Look out for times when people don’t argue that you’re wrong, just that the idea/topic is taboo.
• Time and Space: Try looking at the past for things that used to be acceptable but are now unthinkable.
• Prigs: Imagine comparing what a savvy old man knows about the world compared to a well-behaved sixteen year old girl from the suburbs. He knows the world; she knows, or at least embodies, present taboos. Subtract one from the other, and the result is what we can't say.
• Mechanism: If we could understand the mechanism behind how taboos are created, we may be able notice it when it happens. This usually involves a moderately powerful group creating the taboo to protect itself.

Why look for these things that are true that we can’t say? Curiosity, truth, it’s good for the brain, and because great work tends to grow out of ideas that others have overlooked.

When you find something you can’t say, make sure you pick your battles. Don’t argue with stupid people. But if you have smart and trustworthy friends, it’s good to discuss it with them.