Full Idea
If there is no substance other than those which are formed by nature, natural science will be the first science; but if there is an immovable substance, the science of this must be prior and must be first philosophy.
Gist of Idea
If only natural substances exist, science is first philosophy - but not if there is an immovable substance
Source
Aristotle (Metaphysics [c.324 BCE], 1026a28)
Book Reference
Aristotle: 'The Basic Works of Aristotle', ed/tr. McKeon,Richard [Modern Library Classics 2001], p.779
A Reaction
For Aristotle science is mainly finding the causes of everything. Does he think physical science is the way to study ethics and politics. Maybe, via essential natures and natural functions.