The following is one of my favorite articles in the Summa Theologiae, ST 1.67.1. I think that, among other things, it identifies a feature of language that is too often overlooked, namely, that some words can be taken figuratively or literally without change in their basic meaning if they are taken figuratively and literally in different senses. I also have a general interest in the theological theme of light.
The translation is mine, and thus rough (practice, one might say); it should be taken with a grain of salt. The Latin is here; the Dominican Fathers translation is here.
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Thus we proceed to the first.
It seems that light is properly said of spiritual things. Thus Augustine says (Gen. ad Litt. IV) that in spiritual things is a better and more certain light, and that Christ is not said to be light in the same sense that he is said to be stone, but the former properly, the latter figuratively.
Further, Dionysius (Div. Nom. IV) places Light among the intelligible names of God. But the intelligible names of God are properly said of spiritual things. Therefore light is properly said of spiritual things.
Further, the Apostle says (Eph. 5), all that is manifested is light. But manifestation is more properly in spiritual things than in corporeal things. Therefore so also with light.
But against this is the fact that Ambrose (De Fide) places splendor among those things that are said of God metaphorically.
I respond that it must be said that some names are appropriately said in two ways: in one way according to their first imposition, in another way, according to the use of the name. Thus it is clear in the word 'vision' that by first imposition it signifies the act of the sense of vision [ad significandum actum sensus visus]; but according to the dignity and sureness of this sense, this word is extended, according to spoken usage, to all the cognition of the other senses (thus it is said, "Seeing how it tastes" or "seeing how it smells" or "seeing how it is hot") and further to intellectual cognition, as in Matt. 5: "Blessed are the clean of heart, for they shall see God." And similarly this must be said of the word 'light'. For firstly it is instituted to signify what makes manifest in the sense of vision; but afterward it is extended to signify what makes manifest according to any cognition. If, therefore, the word 'light' is taken according to its first imposition, it is said metaphorically of spiritual things, as Ambrose says. But if it is taken according to its spoken usage, extended to all manifestation, it is properly said of spiritual things.
And from this the response to the objections is clear.
UPDATE: Corrected several typos; and fixed a mistranslation of 'certior' and improved (although not entirely to my satisfaction) the translation of the above Latin phrase (thanks to Ocham for pointing out both of these weaknesses in the original post).
