“It is reasonable to suppose, pace Eusebius, that a similar meaning, viz. ‘of the same nature’, was read into the homoousion. But if this is granted, a further question at once arises: are we to understand ‘of the same nature’ in the ‘generic’ sense in which Origen, for example, had employed ὁμοούσιος, or are we to take it as having the meaning accepted by later Catholic [i.e. Western] theology, viz. numerical identity of substance? The root word οὺσία could signify the kind of substance or stuff common to several individuals of a class, or it could connote an individual thing as such…Indeed, the doctrine of numerical identity of substance has been widely assumed to have been the specific teaching of the Nicene Council. Nevertheless there are the strongest possible reasons for doubting this. The chief of these is the history of the term ὁμοούσιος itself, for in both its secular and its theological usage prior to Nicaea it always conveyed, primarily at any rate, the ‘generic’ sense.”

J.N.D. Kelly, Early Christian Doctrine, pages, 234-235