First, a remark on the doctrine of the states of being. The individual domain in which we move and interact with other individual beings is the result of the conjunction of form and matter, and for this reason it is also called the ‘formal’ domain. The individual domain is further subdivided into the subtle and the corporeal orders. The corporeal order includes the ‘matter’ we can touch and hold, and is the only order acknowledged by modern science. The subtle order has a similar structure but a different kind of matter, sometimes called ether. Beyond the individual domain (subtle and gross) is the supra-individual domain which includes the essences or archetypes of things. We say that these are ‘supra-individual’ because they are never clothed with form and so never individuated. When a form is joined with matter, we are dealing with a process of ‘individuation,’ which is to say the production of a particularized specimen of a supra-individual essence within the individual domain: in this situation, the form represents the archetype or essence and impresses its qualities on the matter in which it ‘inheres.’ Matter is thus the ‘principle of individuation’ because each individual is made unique only by the matter it possesses, whereas all men are identical in terms of form. All men possess the form of man, but all men are individuals by their matter, which is unique to each union.
To bring this back to our discussion, what we call a species is one of the supra-individual archetypes, and all of the beings belonging to a species are particularized specimens of the archetype, individuated by their matter but not by their form, which is possessed in its entirety by all members of the species. The shared form conveys to each individual the qualities of the archetype, even if these qualities express themselves differently and in varying degrees depending on material conditions such as time, place, and development.