A being not only has properties and (with some exceptions) belongs to one of the ten greatest kinds, it also, and most importantly, has existence (esse). Medieval philosophers have a rich understanding of the nature of existence and its interplay with the features that make a being what it is (i. e., the being’s essence). We can only mention some of the general features of this rich tradition.
Many medieval thinkers felt the need to distinguish between the mode of existence that a concrete individual has and the mode of existence that this individual’s constituents and ingredients has. One motivation seems to be this. If the constituents of an individual possessed the same mode of existence as the individual itself, then these constituents would exist in their own right - that is, they would be per se beings. But Aristotle claimed that no substance is composed of substances, which many medieval philosophers interpreted as the claim that no per se being is a composite of actual per se beings. A per se being is something that is truly one and capable of independent existence. But how could something be independent and truly one if its parts themselves are also independent and truly one? It appeared, then, that if x is composed of per se beings, then x is merely one in a weaker or accidental sense - it is an aggregate of substances, not itself a substance.
One strategy was to distinguish between actual existence and potential existence. A human body is made out of the four elements, but when the human body actually exists, these ingredients only potentially exist in the body. They exist in potentiality, since upon death the body is resolved back into the four elements. Hence, in one sense, the elements are not parts of the body.
But some of the items that play a role in the creation of an individual must continue to be present in the individual, when the individual exists. In particular, the nature or essence of the individual must exist in the individual when it exists. Otherwise, the individual would not be what it essentially is. One strategy, which is very old, is to distinguish between the mode of existence that the nature has in itself and the mode that it has in the material world. Boethius, for example, claimed that natures in themselves merely ‘‘subsist,’’ whereas concrete instances of the nature ‘‘substand.’’ It is only when something substands that it can be the subject for accidental properties - that is, to be an individual, material substance. The details of Boethius’ theory are a bit obscure, but it appears that he was espousing a Neoplatonic theory of individuals. The nature itself is a separately existing Form. This Form is then copied in matter. These chunks of matter imprinted with the copy of the Form are those things that substand. The matter and the copy of the Form are parts of the concrete individual, and indeed they are essential parts of the individual, but they are not themselves per se beings. The matter needs the copy of the Form to be something, and this copy of the Form needs to be enmattered in order to be a copy of the Form.
The dominance of Aristotelian philosophy in the Scholastic period meant that most philosophers rejected the Platonic conception of separately existing essences. Essences were only found in the mind or in individual beings. Given that the essence contributed to the existence of the individual, there was still the need to distinguish between the mode of existence of the essence as such and the individual. The Avicennian answer was to distinguish between the essence in itself and the essence in an existent. The essence considered in itself did not exist. It only had existence in so far as it was an essence in the mind or an essence in this individual.
Avicenna, nonetheless, allowed for the essence to have some measure of mind-independent reality, for in itself it was indifferent with respect to this individual or that one. Avicenna’s position did not sit well with Scholastic thinkers, for in their view, if the essence itself had some sort of mind-independent reality, then in effect it has a minor form of existence. And if it has a minor form of existence, then the essence should have a minor form of unity. Generally speaking, there were two solutions to this dilemma: either deny that that essence in itself had any existence at all, or accept that the essence had a minor form of being, and hence a minor form of real unity. Aquinas chose the former strategy; Duns Scotus chose the latter strategy.
World History
