Knowledge & Reasons
Joe Cruz gives an evolutionary account of them.
Epistemologists are philosophers who seek to understand what knowledge is, whether we have any of it, and whether, perhaps, we can improve our ability to gain more of it. ‘Knowledge’ is understood here in a general sense. Particular bits of knowledge – for instance, knowing that 7+5=12, or how to knit mittens, or that George Washington was the first President of the United States – are treated as data. Epistemologists ask, what makes possession of each of those bits of data instances of knowledge, as opposed to merely opinion?
There is a difference between having knowledge and merely having an opinion even if the opinion is correct or useful. After all, one could have a true opinion accidentally, by, say, correctly guessing.