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generation and corruption. Therefore the firmament was not made on the second day.
_On the contrary,_ It is written (Gen. 1:6): "God said: let there be a firmament," and further on (verse 8); "And the evening and morning were the second day."
_I answer that,_ In discussing questions of this kind two rules are to be observed, as Augustine teaches (Gen. ad lit. i, 18). The first is, to hold the truth of Scripture without wavering. The second is that since Holy Scripture can be explained in a multiplicity of senses, one should adhere to a particular explanation, only in such measure as to be ready to abandon it, if it be proved with certainty to be false; lest Holy Scripture be exposed to the ridicule of unbelievers, and obstacles be placed to their believing.
We say, therefore, that the words which speak of the firmament as made on the second day can be understood in two senses. They may be understood, first, of the starry firmament, on which point it is necessary to set forth the different opinions of philosophers. Some of these believed it to be composed of the elements; and this was the opinion of Empedocles, who, however, held further that the body of the firmament was not susceptible of dissolution, because its parts are, so to say, not in disunion, but in harmony. Others held the firmament to be of the nature of the four elements, not, indeed, compounded of them, but being as it were a simple element. Such was the opinion of Plato, who held that element to be fire. Others, again, have held that the heaven is not of the nature of the four elements, but is itself a fifth body, existing over and above these. This is the opinion of Aristotle (De Coel. i, text. 6,32).
According to the first opinion, it may, strictly speaking, be granted that the firmament was made, even as to substance, on the second day. For