I will give you my favorite definition, given to me by my friend Bruno Marchal, a brilliant mathematician from Brussels who spent his life thinking about such topics:
"Consciousness is that which cannot be doubted."
It felt insufficient when he told me, but now I am convinced. It may require some introspection to "get it". It did for me.
Cogitoist propaganda. The appearance of thought is not necessarily the same as thought, so you don't actually know you think just because you believe you think. The cogito (I think therefor I am), like your statement, is incoherent.
LLMs will swear up and down (with a prompt) that they are thinking beings, therefor "they are". They are not ontological actors because of their appearance of doubting their own existence. That's not thought!
The fact that there is experience at all, the contents of which may be “doubted”, cannot be doubted.
I’m not unequivocally claiming this but that’s the thrust of the argument.
I'm sure Bruno is brilliant. But I still don't know what consciousness is. And I think that "definition" doesn't meet the modern scientific standard. And I strongly oppose the idea that in order to learn science I should have to spend time introspecting.
If consciousness isn't a physical process, then you've lost me again. People have discussed these things for hundreds of years.
Yeah, there's not a lot down there, mostly your assumptions about your sense inputs corresponding to some kind of causally consistent external reality. It's the same region as the lead up to what you seem to take as an axiom, "Justified belief about reality has to be based on measurement".
This is not actually a proof. It is, however, exactly the kind of soft reasoning that motivates reasonable axioms. I'm not saying it's a bad axiom, I'm saying you should know what you're doing. That way when you run into a domain where it doesn't apply very well, you know where and how to back up and restart.