What is inside matter?

Our goal is the causes, principles, and elements of substances.

Some substances are recognized by everyone. But some have been advocated by particular schools. Those generally recognized are the natural substances:

• fire, earth, water, air, &c.
• the simple bodies
• plants and their parts
• animals and the parts of animals
• the physical universe and its parts

Others say that Forms and the objects of mathematics are substances.

Others say that there are other substances, the essence and the substratum.

In another way:

• the genus seems more substantial than the various species,
• the universal seems more substantial than the particulars,
• the universal and the genus the Ideas are connected
  • In the same way, they are thought to be substances.

The essence is substance. The definition is a formula of the essence.

This is why we have discussed definition and essential predication.

Since the definition is a formula, and a formula has parts, we had to consider:

• the notion of ‘part’
• what are parts of the substance and what are not
• whether the parts of the substance are also parts of the definition.

Neither the universal nor the genus is a substance.

What about the Ideas and the objects of mathematics?

• Some say these are substances as well as the sensible substances.

The substances are sensible things that all have matter.

The substratum is substance, and this is in one sense the matter (and by matter I mean that which, not being a ’this’ actually, is potentially a ’this')

In another sense, the formula or shape (that which being a ’this’ can be separately formulated),

thirdly the complex of these two, which alone is generated and destroyed, and is, without qualification, capable of separate existence; for of substances completely expressible in a formula some are separable and some are separable and some are not.

But matter is also substance.

For in all the opposite changes that occur there is something which underlies the changes, e.g. in respect of place that which is now here and again elsewhere, and in respect of increase that which is now of one size and again less or greater, and in respect of alteration that which is now healthy and again diseased.

Similarly in respect of substance there is something that is now being generated and again being destroyed, and now underlies the process as a ’this’ and again underlies it in respect of a privation of positive character. And in this change the others are involved.

But in either one or two of the others this is not involved; for it is not necessary if a thing has matter for change of place that it should also have matter for generation and destruction.

The difference between becoming in the full sense and becoming in a qualified sense has been stated in our physical works.