Such an inference would require the method of hypothesis — inference to an unobserved entity.

Mill calls this insight “one of great weight and significance, which impresses a character on the whole mode of philosophical thinking of whoever receives it” (Examination, IX: 11). The doctrine ultimately pushes Mill towards Idealism. One might hold that, though we are only familiar in experience with mental impressions, we can nevertheless infer the existence of non-mental objects lying behind such mental objects. But such an inference could not be supported within experience by enumerative in