ood by us, through their material effects.

Obj. 4: Further, the only cause which cannot be comprehended through
its effects is that which is infinitely distant from them, and this
belongs to God alone. Therefore other created immaterial substances
can be understood by us through material things.

_On the contrary,_ Dionysius says (Div. Nom. i) that "intelligible
things cannot be understood through sensible things, nor composite
things through simple, nor incorporeal through corporeal."

_I answer that,_ Averroes says (De Anima iii) that a philosopher
named Avempace [*Ibn-Badja, Arabian Philosopher; ob. 1183] taught
that by the understanding of natural substances we can be led,
according to true philosophical principles, to the knowledge of
immaterial substances. For since the nature of our intellect is to
abstract the quiddity of material things from matter, anything
material residing in that abstracted quiddity can again be made
subject to abstraction; and as the process of abstraction cannot go
on forever, it must arrive at length at some immaterial quiddity,
absolutely without matter; and this would be the understanding of
immaterial substance.

Now this opinion would be true, were immaterial substances the forms
and species of these material things; as the Platonists supposed.
But supposing, on the contrary, that immaterial substances differ
altogether from the quiddity of material things, it follows that
however much our intellect abstract the quiddity of material things
from matter, it could never arrive at anything akin to immaterial
substance. Therefore we are not able perfectly to understand
immaterial substances through material substances.

Reply Obj. 1: From material things we can rise to some kind of
knowledge of immaterial things, but not to the perfect knowledge
thereof; for there is no proper and adequate proportion between
material and immaterial things, and the likenesses drawn from
material things for the understanding of immaterial things are
very dissimilar therefrom, as Dionysius says (Coel. Hier. ii).

Reply Obj. 2: Science treats of higher things principally by way of
negation. Thus Aristotle (De Coel. i, 3) explains the heavenly bodies
by denying to them inferior corporeal properties. Hence it follows
that much less can immaterial substances be known by us in such a way
as to make us know their quiddity; but we may have a scientific
knowledge of them by way of negation and by their relat