Philosoraptor

Yes but nothing is involved in it, since you think about people thinking about nothing.In order to really think that, you must first conceive nothing.

I didn't realise that the reason people said "You can't think about nothing" was because it is impossible to conceptualise. I don't think that's true. Our mind is abstract enough to conceive of concepts that we don't completely perceive experientially.

I thought the reason why people say "You can't think about nothing" was an indication of the constant activity of the brain.

Yes, we can conceive things we don't perceive experientially. But the problem is that nothing is not a thing, it's a nonsense. Speaking about "nothing" is like speaking about a "square circle". We can't conceive a square circle, because a square circle has nothing to be conceived. We speak about it because we can conceive "square" and "circle" separately, and then we say : "let's say we join the two properties in one being". But we can't.
And when we speak about nothing, it's because we can conceive "no" and "thing" separately.