 As noted above, Mill claims not only that enumerative induction is a valid principle, but that it is the sole principle by which we are justified in inferring unobserved facts about the world.  [2]  In particular, he rejects the independent validity of the “Hypothetical Method”—what has come to be known as inference to the best explanation (System, VII: 492). We are not entitled, that is to say, to believe in something unobserved solely on the basis that it explains the observed facts (Skorupski 1989: 197–202; see also Macleod 2016; Jacobs 1991). A hypothesis 