Epistemology: What is the difference between a priori and a posteriori knowledge?

A priori knowledge is knowledge that can be obtained without experience of the outside world- your internal thoughts alone can provide you with a priori knowledge.A posteriori knowledge is knowledge that can only be obtained through experience of the outside world. For example, the proposition that 'all bachelors are unmarried men' is an a priori proposition because you do not need to meet a bachelor to know that he is unmarried. You can work out he is unmarried purely by thinking about it. On the other hand, the proposition that 'the sun is shining' is a posteriori because in order to know that the sun was shining you would have to experience it through sight, touch etc. Without experiencing the sun shining, you could never 'know' it was shining. You would merely 'believe' it was shining.