There really is no such thing as absolute certainty, but there are plenty of uncertainty's. Everything can change with any small amount of new information that gets added to an equation.
My list of absolute certainty's.
- Nothing.
My list of absolute uncertainty's.
- Everything.
There is one thing, and only one thing, that you can be certain of and Caitlin indeed named it in so many words.
Cogito, ergo sum. That you are conscious cannot be doubted. To doubt it would only confirm it. Caitlin, as Descartes before her, is exactly right that one's own concsiousness is the only thing that cannot be an illusion.