We have now sketched the principles of change: matter, form, and privation. We have seen that change is either substantial or accidental. With this preparation we may turn to the structure or composition of corporeal substances. Not that the study of change has not already given us an insight to the make-up of natural things, but that we shall now focus attention on the make-up which change supposes and again induces. Change, after all, does not take place in a vacuum. It begins with something and ends with something else. What does it end with? What, in other words, are the intrinsic principles of being? This is our question.
Of the three principles enumerated, one is, so to speak, negative, denoting simply the absence of a receivable determination. This is privation. Though not a real entity itself, privation implies something real, namely, the aptitude of the subject to receive the contrary of what it has.12 Privation, therefore, is not a constitutive principle of a natural being, only a principle or condition of its becoming, a starting point. One cannot become what one is, nor what one has not the capacity to become. On the other hand, what is not part of oneself is not a constitutive principle of one's being. Accordingly, only matter and form are intrinsic or component principles of a natural being.
The matter-form composition, however, appears on two levels: It exists in the union of prime matter and substantial form, which are the essential principles of natural being and are involved in substantial change, the change that results in the complete transformation of one substance into another.
It exists also in the union of second matter and accidental form, which is to say, between a substance and its accidents, second matter being the underlying substance that is al- ready composed of prime matter and substantial form. This is the union affected by accidental change, when one accident succeeds another, or at the very least, when an accident is gained or lost, the substance remaining the same.
On this second, and secondary, level matter and form have analogical meaning and are applied to widely differing compositions of being. So, in Aristotelian thought, the matter-form relationship variously exists between the bronze and the statue into which it is cast, between the materials of a building and the arrangement they assume in the completed edifice, between letters of the alphabet and the syllable made of them. These are only a few of many possible examples. Even between the basic elements and their "mixtures" or compounds one may see a matterform relation.
The primary meaning of matter and form, however, is not in these analogical applications but respectively in that matter which is called prime and in that form which is called substantial, and again in the composite thereof. So, what is prime matter, what substantial form, and what the composite?