Moral certainty

If I was subjectively certain about something, and was unable to see how I might be wrong, would I have a proof? We would suppose not, although this is the context of Cartesian anxiety.

What if no-one else could see how I might be wrong either? Even after considerable discussion and investigation?

At some point, out investigations would convince us that we could only be wrong if we had made some general mistake about the possibility of demonstration - about how to talk intelligibly about the object of my certainty. Might this also be a mistaken conclusion?

This kind of structure of doubt applies to groups as well as to individuals, but it has a limit. If we can pose the question, and make no more assumptions in our proof than those that are required to make the posing of the question possible, then we have a different kind of demonstration - it's structure is 'we know the answer if we can ask the question'. (Some obvious questions - 'can we ask questions?' - can be answered very directly this way.)

Can we have a hypothetical attitude to our participation in a conversation? We obviously can't express this within the conversation ("I'm not sure whether we are actually able to talk to each other") because we would be saying that we didn't know what the meaning of this sentence token was. If we were, we could not seriously express the doubt (or we'd by lying if we pretended to - another way to end the conversation ...)

We obviously can't 'privately' ask a question that we can't ask publicly. This would require a private language. We can be 'mad' - we can fail to engage in conversations in a humanly recognisable way. Or we can appear to talk nonsense to any potential interlocutor.

No one could say of our madness:  'they suffer from Cartesian anxiety', except provisionally, and perhaps poetically.  The only positive demonstration of such a thing would be our articulation of it, which would prove it false.