Tertio, pro sufficientia huius divisionis hanc generalem propono apud Aristotelem satis notam: Decima Quinta conclusio. Numquam pluralitas est ponenda sine necessitate. Cum igitur nulla necessitas appareat ponendi plures ordines essentiales primos quam duos praedictos, illi soli sunt.
"Third, for the sufficiency of this division [of essential orders] I propose this general [principle], well known to Aristotle: the Fifteenth conclusion: Plurality is never to be posited without necessity. Since therefore there is no apparent necessity of positing more essential orders than the two already spoken of, they are the only ones."
--Bl Scotus, De Primo Principio, chapter 2.
Ockham is widely credited with the invention of his Razor, otherwise known as the principle of parsimony. People who know better are accustomed to note that Ockham did not in fact discover the principle; it's just that he thought far less was necessary to explain reality than others did, prefering instead a slick, clean, pared-down design for his ontology, transfering all the complicated gadgetry to the mind. Sometimes they credit the Bl Duns with inventing it--occasionally with the hint that he didn't find enough uses for his tool, given the general impression that his is one of the more intricate metaphysics. This praise is also undeserved, however, since I seem to recall that it can also be found somewhere in St Thomas (please don't write in asking for referencs). Besides that, however, Duns does not think he's enunciating something new, but says that it was "known to Aristotle well enough."
I don't know that Aristotle states the principle in so many words. Bl John Duns may in fact be the first to give it an explicit expression. But it would be a mistake to attribute extremely universal principles to any one in particular, and if we do, it might as well be to Aristotle, the archetypal philosophus. Philosophy should aspire to discovery, not to invention, and tend to modesty rather than overreaching in its claims. All philosophers ought to be careful that what they posit has sufficient grounds, and distinguish between positing and hypothesizing, between reasoning and speculation. We should call this tool (not exactly a metaphysical principle so much as a methodological one) our "Philosopher's Razor."
