Full Idea
The evidence lies at the periphery of the [metaphysical] system and runs in from there, through decreasingly specific accounts of the data, to the central ontology.
Gist of Idea
Metaphysics generalises the data, to get at the ontology
Source
John Richardson (Nietzsche's System [2002], Intro)
Book Reference
Richardson,John: 'Nietzsche's System' [OUP 2002], p.7
A Reaction
Philosophy is the study of high level generalisations, IMHO. Studying them means studying the reasons for asserting them. Richardson puts it very nicely.