Product warning first: While I'm interested in philosophy and I have read in the area, I'm by no means and expert and if I say dumb things be gentle with me. How certain can we be that what we think we know is really true? My personal position is that I suspect that there is very little that I can be absolutely certain of. I'm not even absolutely certain of my last sentence. It's not as simple as being absolutely clueless or absolutely certain either. There is a sliding scale of probability (in my mind) that certain assertions I make may be true. I would say, for example, that the fundamentalist Christian conception of God has quite a low probability of being true. (let's say less than 10%). I could still be wrong which would be a shame. OTOH, I'm relatively sure an external world really exists. (Over 95%) But I can always think of loopholes, possibilities that could make me wrong. In fact for me 'I could be wrong' is a centrepiece of my approach to life and other people. There's a downside to this: I find claims to absolute certainty in other people irritating. I fight this tendency constantly. This is the internet. I'm sure we've all seen people who believe passionately in patently absurd things. How do we feel about claims to certainty?