Aristotle begins his Physics, which his philosophy on the first principles of scientific discourse in the following way:
In any subject which has principles, causes and elements, scientific knowledge and understanding stems from a grasp of these.
For we think we know a thing only when we have grasped its first causes and principles and have traced it back to its elements.
It follows obviously that if we are to gain a scientific knowledge of nature as well, we should begin by trying to decide on its principles.
This doesn't entail reductionism, say in the sense that everything is related directly to a single axiomatic foundation.
What it does entail is:
The natural way to go about this is to start with what is more intelligible and clear to us and move from there to what is clearer and more intelligible in itself. For the fact that something is more intelligible to us does not mean that it is intelligible tout court.
So it's a clarification, and a discovery of principles; and one that is constituted naturally in relation to the subject matter at hand.
The question then is, say we have several subjects to hand: say biology and physics, what is their relation? That there must be a relation is obvious; but should this relation entail that one is reduced to the other?
Not neccessarily, for opposites are related and neither, obviously can be reduced to the other (but it can be enlargened, for black and white are opposites, but the species colour contains them).
But this does not deny that an aspect of one can be reduced to another; Aristotle elaborates that the Ionian Monists as supposing that:
it may be possible for everything to be made of the same stuff; this ... is the sense in which natural scientists say that everything is one.
Not that all is alike in species; alike in kind - the subject matter of zoology is different from physics, say; they are different species of knowledge; and the same goes for poets and physicists - as one might find if one set a physicist to write a poem and find they write doggerel, or set a poet to think through a physical concept, like relativity but his wilful will, will not; his soul subtending an angle and aching and arcing through sensual music - the music of sense - to the firmament of some absolute.
More could be written from this angle, emergentism as a kind of becoming - say ...