In modern times consistent empiricists have said this, but it is not a position possible to one who had passed twenty years in association with the mathematicians of the Academy, and Aristotle’s theory only begins in naturalism to end in Platonism. We may condense its most striking positions into the following statement. By science we mean _proved_ knowledge. And proved knowledge is always "mediated"; it is the knowledge of _conclusions_ from premisses. A truth that is scientifically known does not stand alone. The "proof" is simply the pointing out of the connection between the truth we call the conclusion, and other truths which we call the premisses of our demonstration. Science points out the _reason why_ of things, and this is what is meant by the Aristotelian principle that to have science is to know things through their _causes_ or _reasons why_. In an ordered digest of scientific truths, the proper arrangement is to begin with the simplest and most widely extended principles and to reason down, through successive inferences, to the most complex propositions, the _reason why_ of which can only be exhibited by long chains of deductions. This is the order of logical dependence, and is described by Aristotle as reasoning _from_ what is "more knowable in its own nature,"[#] the simple, to what is usually "more familiar to _us_," because less removed from the infinite wealth of sense-perception, the complex. In _discovery_ we have usually to reverse the process and argue from "the familiar to us," highly complex facts, to "the more knowable in its own nature," the simpler principles implied in the facts. [#] This simple expression acquires a mysterious appearance in mediæval philosophy from the standing mistranslation _notiora naturæ_, "better known to nature." It follows that Aristotle, after all, admits the disparateness of sense-perception and scientific knowledge. Sense-perception of itself never gives us scientific truth, because it can only assure us that a fact is so; it cannot _explain_ the fact by showing its connection with the rest of the system of facts, "it does not give the _reason_ for the fact." Knowledge of perception is always "immediate," and for that very reason is never scientific. If we stood on the moon and saw the earth, interposing between us and the sun, we should still not have scientific knowledge about the eclipse, because "we should still have to ask for the _reason why_." (In fact, we should not know the reason _why_ without a theory of light including the proposition that light-waves are propagated in straight lines and several others.) Similarly Aristotle insists that Induction does not yield scientific truth. "He who makes an induction points out something, but does not demonstrate anything."