it is understood. Therefore in things without matter, such as
the angels, the medium whereby the object is understood is the very
substance of the one understanding it.

Obj. 3: Further, everything which is contained in another is there
according to the mode of the container. But an angel has an
intellectual nature. Therefore whatever is in him is there in an
intelligible mode. But all things are in him: because the lower
orders of beings are essentially in the higher, while the higher are
in the lower participatively: and therefore Dionysius says (Div. Nom.
iv) that God "enfolds the whole in the whole," i.e. all in all.
Therefore the angel knows all things in his substance.

_On the contrary,_ Dionysius says (Div. Nom. iv) that "the angels are
enlightened by the forms of things." Therefore they know by the forms
of things, and not by their own substance.

_I answer that,_ The medium through which the intellect understands,
is compared to the intellect understanding it as its form, because it
is by the form that the agent acts. Now in order that the faculty may
be perfectly completed by the form, it is necessary for all things to
which the faculty extends to be contained under the form. Hence it is
that in things which are corruptible, the form does not perfectly
complete the potentiality of the matter: because the potentiality of
the matter extends to more things than are contained under this or
that form. But the intellective power of the angel extends to
understanding all things: because the object of the intellect is
universal being or universal truth. The angel's essence, however,
does not comprise all things in itself, since it is an essence
restricted to a genus and species. This is proper to the Divine
essence, which is infinite, simply and perfectly to comprise all
things in Itself. Therefore God alone knows all things by His
essence. But an angel cannot know all things by his essence; and his
intellect must be perfected by some species in order to know things.

Reply Obj. 1: When it is said that the angel knows things according
to his own nature, the words "according to" do not determine the
medium of such knowledge, since the medium is the similitude of the
thing known; but they denote the knowing power, which belongs to the
angel of his own nature.

Reply Obj. 2: As the sense in act is the sensible in act, as stated
in _De Anima_ ii, text. 53, not so that the sensitive power is the
sensible object's l