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I’ve seen a lot of experimental evidence for that. "All unicorns are blue" is logically equivalent to "all non-blue things are not unicorns".

Over the past few decades I’ve seen ten of thousands of non-blue things, and none of them were unicorns!

https://en.wikipedia.org/wiki/Raven_paradox

Contrapositives are one of my favorite things in simple logic to demonstrate the difference between rigorous logic and our human heuristic logic. Mathematically, contrapositives are identical to the original statement, but extremely frequently, if not almost always, they sound different to us humans.

If more people understood them, there's a number of dumb internet debates that could finally die, where X -> Y isn't immediately obviously wrong to our human brains and may even sound correct but !Y -> !X is immediately obviously wrong.

> All unicorns are blue, aren't they?

Indeed they aren't! All unicorns are not blue.

True

All unicorns are blue, indeed.

The surprising thing is that all unicorns are red, too.

I'm not sure, but all unicorns I've seen have been blue.