isdom. Now it would ill become the Divine wisdom
to make afterwards that which is naturally first. But though the
firmament naturally precedes the earth and the waters, these are
mentioned before the formation of light, which was on the first day.
Therefore the firmament was not made on the second day.

Obj. 3: Further, all that was made in the six days was formed out of
matter created before days began. But the firmament cannot have been
formed out of pre-existing matter, for if so it would be liable to
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 it is part of the work of creation to produce the substance of the
elements, while it belongs to the wo