Is there anything we can know for sure?

And he wouldn't shave himself, even if he was a barber.

Rap

How about immediate sensory experience? It's the interpretation of that experience that is doubtful, especially the presupposition that there is an agent of that sensation.

I'm not sure if my mind recognizes the same 'red' a your mind. Sensory experience varies all over the place--and I'm synthesthetic so there's that additional cat to throw in the bag.

IMHO the only thing we can know for sure are constructs--a right triangle in a plane follows pythagoras, that is provable. Every thing else is open to some degree of skepticism.

Rap

Accuracy is just conforming to the current standards set in formal systems of knowledge or effective practices (the kind whose content is produced and approved by widely accepted methods / procedures rather than arbitrary thoughts and beliefs). There may also be intuitive facts and templates that are provided innately for knowledge-formulating agents, boxes which they can't escape from without running into problems. Like, events are definitely presenting themselves, in order that anything can be claimed to be known as existing or be happening / have happened (including the claiming).

I'm sure of MY redness experience. It's a subjective certainty. As a synthesthetic you may hear your redness with certainty. Notice that there is only room for disagreement between us in our after-the-fact interpretations of our sensory experiences.
Our felt certainty may even disappear after our experiences, but not while they exist (as realities). What about using (subjective) Truth and Reality interchangeably?
Only immediate experience is "certain", even mirages--i.e., they are real, actual experiences--they are real mirages. It's the interpretation of them as water, or whatever, that makes them delusional. Seeing a mirage and realizing at that moment that it is an optical illusion is a moment of wisdom.

The principal delusion is the tacit and imperious notion that there is a subject of all experience. My reference to "my" redness experience is seen to be delusional (actually a demand of our grammar) if we reject, as I do the cartesian distinction between "me" and "all else". Bettter that I eliminate "my" (with its reference to a fictional ego/subject) and just say "the experience of redness is filled with the sense of certainty...."

Decartes answered this question the best: "I think, therefore I am."

He should have said, "'I' think therefore there's thought."

Hate to cross over from post to another but there IS something I know for sure (and remember "certainty" is an emotional state): I know nothing for sure.

true

but my point still stands

The only 'truths' are constructions.

Absolutely transcendental and imaginary, proof and truth is absolute, once found. The weird thing is how well they sometimes work in the physical world.

Rap

we cannot be completely sure about anything. we can only raise probability by researching, experiencing.. but the certainty will never be 100%, that's out of our dispositions.
well, the percentage is kind of tricky since it's percepted individually. so it's useless to use percentage. we can just experience, experience and act on the base of our experience, while we might be wrong in all our conclusions

I disagree

the only truths are from experience , observation , knowledge and understanding

But in many cases experience , observation , knowledge and understanding are subjective--yours may be quite different from mine.

In a plane Pythagoras has been proven to be true. The only variations are the methods of proof.

Rap