I shall be mainly concerned with the question ‘What is personal propositional knowledge?’. This question is obviously quite narrowly focused, in three respects. In the first place, there is impersonal as well as personal knowledge. Second, a distinction is often drawn between propositional knowledge and practical knowledge. And third, as well as asking what knowledge is, it is also possible to ask whether and how knowledge of various kinds can be acquired: causal knowledge, a priori knowledge, moral knowledge, and so on. I shall dwell briefly on each of these three points. First, there is the distinction between personal and impersonal knowledge – in other words, between the psychological concept of knowledge and the social one.1 We use the concept of knowledge to describe the cognitive condition of individuals; but we also use it to describe the progress of scientific and historical research. So for example we can speak or enquire about the state of knowledge in a particular field of biology or history. And if we do so, we are evidently not concerned with what anyone in particular knows about, say, the genetics of fruit flies or the career of Charlemagne, but rather with what the scientific or academic community knows. Needless to say, there is a close connection between personal and impersonal knowledge. But ‘It is known that p’ does not simply mean ‘Someone or other.