Definition: The middle is the subject through which the end influences the beginning and through which the beginning reciprocally influences the end, and this subject partakes in the nature of both.
Clarification: Thus, every substantial middle connects a beginning to an end, and as there is no beginning without an end, likewise there is no middle without an end and consequently no middle without a beginning. Hence, the middle is a being aggregated from the likenesses of two very different things, namely its beginning and its end. This is why the middle is an image of its beginning and end where the transit from the beginning to the end is considered and where the influence of the end returns to the beginning, as we said. The middle that is the beginning, middle and end of every other middle is the one in which and through which the beginning and end are one and the same natural essence of goodness, greatness, eternity etc. No other middles lacking these conditions can be supreme, they are all lower middles because their goodness, greatness etc, are greater in the middle than in the beginning, and greater in the end than in the beginning or middle; nor can they even be supreme in the end because they have been produced from lesser things for that end.
Distinctions: The middle is considered in many ways, as it exists in many ways. The medium of conjunction joins diverse or distinct things into one, like the virtue issuing from form and matter joins form to matter in one substantial being whose principles or essences they are while this being is their end, or purpose.
The medium of measurement is like the midpoint of a line equidistant from the ends, or like the center of a circle, equidistant from the circumference, or like something that equally and mutually participates in goodness and greatness, and so forth.
And the middle between extremes is like a line connecting its ends, or like something completely enclosed within a spherical surface, or like goodness that continues in the entire medium passing through greatness, duration, power etc., justice etc., difference, concordance, beginning, middle and end, majority, equality etc. to the last principle.
Now this principle, called the multiple medium, is necessary to this Art. The artist who knows the conditions of the supreme and lesser media can draw conclusions when he knows what medium is proportioned to the beginning and its end as the beginning's virtue transits through its middle to its end.
Privation of the principle described here entails the privation of whatever exists, namely of every cause, every perfection and every effect, and consequently of everything that is.
Nature: Its fullness is in the mediator, mediable and the act of mediation.