arguments showing that what is proposed to our faith is not
impossible, or else they are proofs drawn from the principles of
faith, i.e. from the authority of Holy Writ, as Dionysius declares
(Div. Nom. ii). Whatever is based on these principles is as well
proved in the eyes of the faithful, as a conclusion drawn from
self-evident principles is in the eyes of all. Hence again, theology
is a science, as we stated at the outset of this work (P. I, Q. 1, A. 2).

Reply Obj. 3: Things which can be proved by demonstration are
reckoned among the articles of faith, not because they are believed
simply by all, but because they are a necessary presupposition to
matters of faith, so that those who do not known them by
demonstration must know them first of all by faith.

Reply Obj. 4: As the Philosopher says (Poster. i), "science and
opinion about the same object can certainly be in different men," as
we have stated above about science and faith; yet it is possible for
one and the same man to have science and faith about the same thing
relatively, i.e. in relation to the object, but not in the same
respect. For it is possible for the same person, about one and the
same object, to know one thing and to think another: and, in like
manner, one may know by demonstration the unity of the Godhead, and,
by faith, the Trinity. On the other hand, in one and the same man,
about the same object, and in the same respect, science is
incompatible with either opinion or faith, yet for different reasons.
Because science is incompatible with opinion about the same object
simply, for the reason that science demands that its object should be
deemed impossible to be otherwise, whereas it is essential to
opinion, that its object should be deemed possible to be otherwise.
Yet that which is the object of faith, on account of the certainty of