 Generally speaking, for a medieval realist the essence of a thing is the main metaphysical component of that thing, namely that in virtue of which that thing is something of a certain kind: a human, a cat, or a stone. Therefore, essences are connected with being taken only in the sense of that which is real, that is to say, actually existing. Since being taken in this sense is divided into the ten categories and is absolutely and primarily said of substances and only secondarily of accidents, essences were usually viewed as something (1) common to a multiplicity of items in virtue of which these various items belong to their species and genera, as humanity is the essence of humans; and (2) present primarily and properly in substances, but in accidents secondarily and derivatively.