Full Idea
The underlying nature is an object of knowledge, by an analogy. For as bronze is to a statue, wood to a bed, or matter and the formless before receiving form to any thing which has form, so is the underlying nature of substance, the 'this' or existent.
Gist of Idea
We only infer underlying natures by analogy, observing bronze of a statue, or wood of a bed
Source
Aristotle (Physics [c.337 BCE], 191a08)
Book Reference
Aristotle: 'The Basic Works of Aristotle', ed/tr. McKeon,Richard [Modern Library Classics 2001], p.232
A Reaction
Scholastics were perfectly aware of this cautious approach. It is only the critics who jeer at Aristotelians for claiming to know all about the essences of things. Essence is like the Unmoved Mover, inferred but unknown.