Chapter Four of the Third Decade
On the power of demons with respect to natural effects, concerning which three little questions will be resolved
Question One of Chapter Four of the Third Decade
Whether a demon can produce a natural effect without seed
It is asked whether demons by their own power, without seeds, can immediately produce some natural effect in matter, such as the form of a worm or serpent.
To this it first appears that one must respond affirmatively.
For whenever certain causes are ordered to one another according to prior and posterior, the first cause influences the thing caused more than the second cause does; and when the influence of the second cause has been removed, the influence of the first cause still remains.
But the power of inferior natural agents, the motion of the heaven, and the influence of an intelligence or separated substance are subordinated in such a way that the heaven is moved by the power of the influence of the separated substance, while these inferior agents act by the power of the heaven.
Therefore, when the operation of the heaven and the action of these inferior natural agents have been removed a form can still be introduced into matter by a separated substance and intelligence. And thus demons and angels will be able to produce a true effect without seminal reasons.
In response it must be said that a twofold error is found concerning this matter.
For there were certain gentiles who believed demons to be gods and believed that they operated in these inferior things by way of creation. But the Master refutes this error in Book II of the Sentences, distinction 7.
There was another error, that of Avicenna, who held that all the forms which are introduced into matter proceed from a giver intelligence.
Thus he held that natural agents did nothing other than dispose matter toward the intelligence.
They set down the example of the rational soul informing the body: in response to a conception of the soul the body is moved immediately, or toward lust at the apprehension of a beloved woman, or toward falling from the imagination of an exterior fall.
Therefore demons and angels will be able much more powerfully and immediately to produce natural effects without seeds.
But this opinion, like the preceding one, is erroneous.
The reason is that, since becoming is the way to being, becoming properly belongs to that to which being belongs. Therefore, the introduction of a form into matter will belong to that from which the whole composite has being and is created.
But the whole composite is created immediately by God alone. Mediately, however, a form is not introduced into matter except by something like itself, through motion and transmutation, because every agent produces something like itself.
A natural agent is composed of matter and form. Therefore neither demons nor good angels can by their own power immediately produce a substantial or accidental form.
To the first argument it must be said that, although a principal agent influences an effect more than a secondary agent does, it nevertheless does not follow that it can always produce the principal effect without an instrument, just as a craftsman cannot produce a chest without an axe.
Therefore, since these effects and substantial forms are naturally apt to be produced by a natural agent through motion, or through creation as by God, a separated substance or demon cannot produce them immediately.
Nor is the example concerning the soul which Avicenna sets down valid, because the soul is not only a mover but also a form, and the motion of the sensitive appetite is also subject to the command of reason.
These things are elicited from Thomas in Book II of the Sentences and from the commentators there.