I'm not asking this loosely; I'm asking it philosophically. To get things a bit more precise, I'm not looking for a list of all the things you know, since that would detain us for too long. No, I'm interested in whether all the things you know are true. You might suppose so since this is what a knowledge claim entails. 'I know that today is 22 September'; 'I know that Cambridge doesn't get as much rainfall as Manchester'; 'I know that there's no highest prime number'; and so forth. On the other hand, 'I know that I can run as fast as Usain Bolt' and 'I know that Karl Marx had a son called Harpo' don't work so well; spoken seriously, they misapply the word 'know' in its standard meaning.
So must everything I know be true? If I really do know it, it seems it must be. I might say that I know something which in fact isn't true, but then I merely thought I knew it when I didn't. It turned out to be a false belief.
However, Susan Krantz Gabriel throws a spanner in the works here by explaining that most of us know that amongst the things we know there will be some propositions that later turn out to have been false. Are we to say, therefore, that we only ever think we know what we know? Or should we, rather, accept that within the mostly secure body of knowledge we go about with there are some things we know that are false beliefs?
I don't know about you, but I'm going for a lie-down.