IN Book I. (n. 60) we have shown that God, because of His self-existence, is necessarily One undivided Being, and thence we have inferred that this One self-existent Being must be infinite. (n. 68.) The same conclusion, viz., that God is One and Infinite, may be reached in an inverse order by evincing first that self-existence involves Infinity, and then arguing from the Infinity of the self-existent to its Unity. To bring out the absolutely necessary connection of Infinity with Self-existence, we may choose one or other of the following two methods of proof:
(1) A self-existent nature is manifestly incapable either of development or of diminution of its actual perfection. For as it is uncaused being, the manner of its existence must be as constant as its unchangeable essence. Consequently, whatever perfection can be conceived as compatible with its essence, must actually and for ever be contained in that essence. Otherwise, we should be bound to conceive in it a perfection as possible which at the same time was absolutely not realizable, and consequently intrinsically contradictory.
This much granted, it is evident that the concept of self-existence, expressing as it does absolute positive being, is not opposed to any perfection whatever, for every perfection is positive being. It follows then that every perfection is actually contained in a self-existing Nature, in other words, such a nature is infinitely perfect.
(2) It has been proved (n. 29, seq.) that the soul of man has for its First Cause a self-existent intelligent Being. Now the human soul is naturally adapted to the knowledge of Truth and the love of Goodness, and may be improved indefinitely in both these perfections. Consequently its First self-existent Cause cannot lack either of them. Neither can it possess them as perfections capable of improvement. To admit this would be tantamount to granting that its way of existence was not due to its essence alone -- a concession that destroys the very notion of Self-existence. Hence it is evident that the capability of indefinite improvement in the knowledge of Truth and the love of Goodness innate in the human mind has its ultimate sufficient reason in a self-existent Mind which knows all Truth, and loves all Goodness, without being determined thereto by any influence from without. But actual and unbounded knowledge of objective Truth, and unbounded love of objective Goodness cannot belong io the Nature of Self-existence, unless the latter coincides with the real source of all objective Truth and Goodness, and consequently is infinitely perfect.
Having thus shown that Self-existence involves Infinity, it is easy to convince ourselves that Infinity cannot belong to more than One Self-existent Being, for if there were several such beings, none of them would be the source of all reality, because none of them would possess the actual perfection by which the rest differed from it. Consequently none of them would unite in itself all conceivable perfections.
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