Works of St. Anselm, tr. by Sidney Norton Deane, [1903], at sacred-texts.com
FURTHERMORE, if one observes the nature of things he perceives, whether he will or no, that not all are embraced in a single degree of dignity; but that certain among them are distinguished by inequality of degree. For, he who doubts that the horse is superior in its nature to wood, and man more excellent than the horse, assuredly does not deserve the name of man. Therefore, although it cannot be denied that some natures are superior to others, nevertheless reason convinces us that some nature is so preeminent among these, that it has no superior. For, if the distinction of degrees is infinite, so that there is among them no degree, than which no higher can be found, our course of reasoning reaches this conclusion: that the multitude of natures themselves is not limited by any bounds. But only an absurdly foolish man can fail to regard such a conclusion as absurdly foolish. There is, then, necessarily some nature which is so superior to some nature or natures, that there is none in comparison with which it is ranked as inferior.
Now, this nature which is such, either is single, or there are more natures than one of this sort, and they are of equal degree.
But, if they are more than one and equal, since they cannot be equal through any diverse causes, but only through some cause which is one and the same, that one cause, through which they are equally so p. 43 great, either is itself what they are, that is, the very essence of these natures; or else it is another than what they are.
But if it is nothing else than their very essence itself, just as they have not more than one essence, but a single essence, so they have not more than one nature, but a single nature. For I here understand nature as identical with essence.
If, however, that through which these natures are so great is another than that which they are, then, certainly, they are less than that through which they are so great. For, whatever is great through something else is less than that through which it is great. Therefore, they are not so great that there is nothing else greater than they.
But if, neither through what they are nor through anything other than themselves, can there be more such natures than one, than which nothing else shall be more excellent, then in no wise can there be more than one nature of this kind. We conclude, then, that there is some nature which is one and single, and which is so superior to others that it is inferior to none. But that which is such is the greatest and best of all existing beings. Hence, there is a certain nature which is the highest of all existing beings. This, however, it cannot be, unless it is what it is through itself, and all existing beings are what they are through it.
For since, as our reasoning showed us not long since, that which exists through itself, and through which all other things exist, is the highest of all existing beings; either conversely, that which is the highest exists through itself, and all others through it; or, there will be more than one supreme being. But it p. 44 is manifest that there cannot be more than one supreme being. There is, therefore, a certain Nature, or Substance, or Essence, which is through itself good and great, and through itself is what it is; and through which exists whatever is truly good, or great, or has any existence at all; and which is the supreme good being, the supreme great being, being or subsisting as supreme, that is, the highest of all existing beings.