D. You will be kind enough to observe what the Catholic Church teaches, that it is the substance of the body and blood of Christ, which is under the modifications of bread and wine.
W. Suppose it is; what difference does that make?
D. All the difference in the world. Pray, what is a substance?
W. It is that part of a being which remains immutable amid all the vicissitudes and changes of the being. These changes or vicissitudes are called accidents or modifications; that which remains always the same and immutable is called substance.
D. Right; and, pray, has substance
any dimensions, has it length, breadth, height, or depth, or is it what philosophers call a simple being?
W. It must have no dimensions, because dimensions may change and vary, and the substance must be always the same.
D. Then substance is a simple being, that is, it has neither height, depth, length, or breadth.
W. So it would seem, and so, if I recollect aright, all the metaphysicians worth the name hold it to be.
D. Right again; and, if you remember, Leibnitz calls it a monas, or a unit, and distinguishes two kinds of substances, the simple and the composite. The simple is one substance; the composite is an aggregate of simple substances or units. Thus, bodies are an aggregate of substances or units.