Something you can know with 100% certainty

A fragment of Escher's RelativityYet another supposedly gotcha question that irrational people often ask in order to unsettle their interlocutor: “can you know anything with 100% certainty?” Well, of course I can, and so can you...

I know with 100% certainty that I don’t know everything. Or that I don’t know the first names of the people who will read this blog post, in the order in which they will. I could go on.

The question is of course totally dishonest as it aims not at getting a honest answer, but at getting you to admit that because nothing is certain (which is wrong), then anything goes and all opinions are equally valid, especially of course the specific silly belief one would like to convince you of.

It tries to conflate “not 100% certain”, which applies to most empirical knowledge, with “unlikely”, or “reasonable to not believe in”. This is of course extremely silly. Asimov said it best:

"When people thought the earth was flat, they were wrong. When people thought the earth was spherical, they were wrong. But if you think that thinking the earth is spherical is just as wrong as thinking the earth is flat, then your view is wronger than both of them put together."

The argument, however, seems to be strangely convincing, despite its obvious flaws, and too often we answer “well, no, of course not” whereas the reasonable answer is “yes, of course I can.” The more interesting and reasonable question that we should ask back is: do you proportion belief to the quantity and quality of available evidence?