Proslogium and Monologium/Monologium/Chapter27

Chapter XXVII
It is not included among substances as commonly treated, yet it is a substance and an indivisible spirit.

It is, therefore, evident that in any ordinary treatment of substance, this Substance cannot be included, from sharing in whose essence every nature is excluded. Indeed, since every substance is treated either as universal, i. e., as essentially common to more than one substance, as being a man is common to individual men; or as individual, having a universal essence in common with others, as individual men have in common with individual men the fact that they are men; does any one conceive that, in the treatment of other substances, that supreme Nature is included, which neither divides itself into more substances than one, nor unites with any other, by virtue of a common essence?

Yet, seeing that it not only most certainly exists, but exists in the highest degree of all things; and since the essence of anything is usually called its substance, doubtless if any worthy name can be given it, there is no objection to our calling it substance.

And since no worthier essence than spirit and body is known, and of these, spirit is more worthy than body, it must certainly be maintained that this Being is spirit and not body. But, seeing that one spirit has not any parts, and there cannot be more spirits than one of this kind, it must, by all means, be an indivisible spirit. For since, as is shown above, it is neither compounded of parts, nor can be conceived of as mutable, through any differences or accidents, it is impossible that it is divisible by any form of division.