However, in order that the statements, which are to be presented, may appear to rest upon a solid and immovable foundation, an exordium may then be assumed with respect to which no rational person ought to be in doubt.
Every extended material substance is composed of substantial parts separate in place or situation. For wood is not only composed of matter and form, which are essential parts and of diverse grounds; but it is also composed of integral parts, of which each is wood. But it is manifest that these parts, of which each is wood, are not in the same situation; therefore, they are separate in situation. And yet wood is truly composed of parts and is not composed of accidents; therefore, it is composed of substantial parts separate in situation.
Again, when wood is divided into two equal parts, no substance new as regards itself as a whole is generated; but there are now two substances really distinct locally; for otherwise, when wood is divided into halves, the accidents would remain without a subject in one half; from which, therefore, no substance new as regards itself as a whole is generated. It is necessary, that those two substances, each of which is a certain whole after division, were previously making one whole wood, and were not at the same time in the same place; therefore, there were before two parts of one total wood separate in situation.
Again, one half of the wood can be corrupted, the other not corrupted; but such a corruption is a substantial corruption; therefore, some substance, which was before, is now destroyed. And it is manifest that some substance, which was before, now remains; therefore, there were before two substantial parts of the same wood composing one wood.
Again, the whiteness existing in the wood is a whole in some whole and part in part; or there is, therefore, a whole in some whole substance and part in part, or there is a whole in some whole accident and part in part. If the first be granted, the thesis is maintained, that there is some substance composed of substantial parts separate in situation, as parts of whiteness are separate in situation and place. If the second is granted, it is necessary to give some primary subject to that accident, so that there may be a whole in a whole subject and a part in a part. And if, indeed, substance be such a subject, I accept the thesis; but if an accident be considered the total subject of that accident; then I inquire about the subject of that (accident) as about the former; and it is necessary to continue the procedure indefinitely, or that there may be some extended accident having some substance for a primary subject, which is a whole in a whole substance and a part in a part, which can not be, unless that substance have substantial parts separate in situation.
Again, unless wood and any material, extended substance could universally have real and substantial parts separate in situation; there could no more be such a substance really extended than there could a rational soul. For as a rational soul is a whole in a whole body and a whole in each part; so any material substance would be a whole under a whole quantity and a whole under each part; but that is absurd. It might be able to be said that there is no similarity, for the soul does not have parts; therefore, it might be able to be argued about knowledge and virtue, which have intentional parts.
Therefore, it remains that an extended material substance has substantial parts locally separate which are to such a degree distinguished from one another, that one part can be destroyed, another not destroyed, and not only this; but even if they remain, they can be mutually separated and can be certain distinct wholes. as when wood or stone is divided, those the same numerically, which were before parts, are now wholes and not parts; yet they are not now other than before.
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