 First, knowledge involves direct apprehension of facts or the inferential apprehension of one fact ‘as necessitated by other facts’, but right opinion is always partly grounded on ‘the product of other psychical events such as wishes, hopes, fears, or the mere association of ideas’ (RG 146). Second, knowledge involves certainty which right opinion lacks (RG 30, 138–139, 147). In addition, ‘knowledge of general principles is intellectually more valuable than knowledge of isolated matters of fact’ and the more general the knowledge – the more it explains or has the potential to explain other facts – the better it is (RG 147; for discussion, see Hurka 2014, 206–208).