Although all real inference, in Mill's opinion, is from particulars to particulars, he was ready to concede that scientific enquiry is normally interested in the establishment of universal propositions — to wit, in the discovery and demonstration of natural laws. Indeed, induction may even be defined, Mill said, as "the operation of discovering and proving general propositions' (SL, p. 284). But this does not mean that the scientist's inferences are different in some fundamental way from the inferences from particulars to particulars which had been described in the second Book of the Logic; for induction in science is merely a "form of the very same process," "generals' being "but collections of particulars, definite in kind but indefinite in number." Where our evidence entitles us to draw an inference about "even one unknown case," wrote Mill, it will also justify us in "drawing a similar inference with respect to a whole class of cases' (ibid.).