This is very naive but has only occurred to me:
- If I were a brain in a vat, I'd expect my experiences to be simple or not very orderly (glitchy); but if I were an ordinary human being as I seem to be, the experiences I would expect would be like that.
- My experiences are complex, continuous and very orderly.
- So, probably, I am an ordinary human being rather than a brain in a vat.
This argument is specific to brains in vats. It might not apply to other sceptical hypotheses.