In how many senses a thing essentially “is” is shown by the forms of the predicate we use in speaking of it, for to be has as many senses as there are forms.

…to be used in an analysis of the objects essential nature, were the following: substance, quantity, quality, relation, time, place, position, state, activity, and passivity.

Ways to define “substance” is “essence”…the essence is the individuality; …essence is composed of those things the enumeration of which makes a definition…to understand anything is to understand its essence.

The requirement for that which by excercise of thought passes from being something potentially to being it actually is that once the change is willed, nothing external must prevent its taking place.