Aquinas: Metaphysics & Epistemology


Doctrines & Discoveries

Notes & Quotes

The Central Problem: reconciling the tenets of Christian Faith with scientific and philosophical insights of classical thinkers -- with Aristotle, in particular



Classical and Christian Views Conflict

Classical View

  • morality is this-worldly: How to get rightly related to yourself and others in society?
  • a human problem solvable by the application of human resources -- reason in particular -- here on earth
  • the problem is how to be happy

Christian View

  • morality is other-worldly: How to get rightly related to God. a problem not soluble by the application of human resources but requiring God's grace. the problem is how to be pious and faithful

Influence of Aristotle

  • his empirical-naturalistic slant contrary to the Neoplatonic mysticism which, through the influence of Augustine had long dominated Christian thinking.
  • heretical doctrines including the eternity of the world &  Averroes  denial of the immortality of the individual soul.

1.        Granted that everyone understands by this name God is signified something than which nothing greater can be thought, nevertheless, it does not therefore follow that he understands that what the name signifies exists actually, but only that it exists mentally. (Aquinas: 219)


The magnitude of Thomas' task

Greek physicists held the world to be "a closed system of naturally caused events"

Christians held the world to be "a stage setting on which the drama of salvation unfolded" open to supernatural input and influences

Greeks: humans have in themselves the necessary intelligence and power to achieve a good and successful life.

Augustine: human nature is fallen: "crooked sordid, bespotted, and ulcerous."

Rebirth of empiricism:

From revelation to rationalism (Anselm)

On toward empiricism (Thomas) {1}

Basic Concepts & Their Application: The Universe as a Hierarchy of Substances &  Form as Actuality




Reason and Revelation

Revealed truths provide the starting points or premises from which we can deduce further conclusions about theology & morality( in particular). {1}

Truths of revelation serve as guides in the actual process of philosophical reasoning about theology & morality (in particular)

Reason cannot contradict revelation, but it can and does supplement it. {2}

Substance is matter made actual by its form.

On beyond Aristotle

humans are natural beings with natural functions (as The Philosopher said) but also spiritual beings, children of God (as revelation reveals)

God is pure intelligence & actuality who inspires the universe's motion (as The Philosopher said) but also Our Father (as revelation reveals)

1.        As the other sciences do not argue in proof of their principles to demonstrate other truths in these sciences, so this doctrine does not argue in proof of its principles, which are the articles of faith, but from them it goes on to prove something else.  (213)

2.        Sacred doctrine also makes use of human reason, not, indeed, to prove faith (for thereby the merit of faith would come to an end), but to make clear other things that are set forth in this doctrine.  Since therefore grace does not destroy nature, but perfects it, natural reason should minister to faith as the natural inclination of the will ministers to charity. (214)

3.        There is, therefore, no reason why another science should not treat of the very same objects, as known by the light of divine revelation, which the philosophical sciences treat of according as they are knowable by the light of natural reason.  (S.T., Ia, 1)

God's Nature


essence: that about a thing which makes it what it is.  Its essential features are those a thing of a kind must possess in order to be.

accident:  a feature a thing of a kind may or may not possess while continuing to be a thing of its kind.


Difficulties about Divine Knowledge of Particulars

          particulars are always changing, so, track particulars knowledge must always be changing; but God is unchanging.

          Some particulars are contingent, but God's knowledge is certain (of what must be), so what merely may be is unknowable to God.

          Real knowledge -- even in humans -- is of universals not particulars.




          Aristotelian realism: forms do not subsist independently (contra Platonism) but only exist in substances, individuals units of formed-matter.

          To know the cause it to know the effect.

         Like causes like.



God is not bodily, not material, not compound

  • Bodies do not move unless moved & God is an unmoved mover; so God is not bodily.
  • What is composed of matter & form is bodily; so God is not composed of matter & form.
  • Compounds are posterior to their parts, and God has already been shown to be the first being.

God is his own essence

  • created individuals, e.g., Socrates are less & more than their essences

less: there being other humans

more: there are his accidents

  • God is the only possible one of his kind & is not subject to accidents (which are materially or externally caused)
  • "We can know that God is that and that He is his own essence, but we cannot know what that essence is." Jones (225)

God is perfect actuality -- all a being can be -- since He has no unactualized potential.{1}

God is good: actuality or being, being what all things strive for or desire, is what's desirable or good. {2}

God is intelligent

God is self-moved

  • self-motion is due to appetite or apprehension {3}
  • appetite is moved by the sensible things perceived as good (desirable): what's moved by appetite is not truly self-moved.
  • only apprehension (or intellect) can apprehend the unadulterated good  which is God himself
  • therefore, God must be moved by his own intellectual self-apprehension, He is intelligent. {4}

God is all knowing

  • Knowledge capability requires immateriality; God is in the highest degree immaterial; therefore God "occupies the highest place in knowledge."
  • Since God is the cause of all things, and to know the cause is to know the effect, God -- since he knows Himself -- knows all things.
  • Knows the particulars (as revelation bespeaks)

since to know the cause is to know the effects

& God's effects are singular things

& God knows himself {7}

God is Volitional

  • Aristotle: The object of will is something the agent lacks & God, since he lacks nothing, wills not.
  • Thomas's Replies:

God wills Himself {8}

in willing Himself God wills all things.

God is Creator {11}

  • To say that God created the world out of nothing is just to say that there is nothing that does not owe its goodness/reality to God.
  • God wills creation out of his goodness, since goodness is inclined to share. {10}

God is Providential & micromanages creation

  • There is no chance (contra Aristotle): every event, being part of God's plan, has a cause.
  • Effects generally proceed from definite secondary causes because God in his goodness has willed the preservation of order in the universe.
  • Miracles occur when God wills to produce an effect directly, without the mediation of secondary causes.  Miracles are outside, but not contrary to, the order of nature.
  • There is genuine contingency, despite the fact that God foresees all that will happen and causes it happen as He foresees, since some of the secondary (or proximate) causes God prepares cause merely contingently not necessarily.  They merely incline but don't determine. {12}

1.        Just as matter, as such, is merely potential, so an agent, as such, is in a state of actuality.  Hence the first active principle must needs be the most actual, and therefore most perfect; for a thing is said to be perfect in proportion to its actuality. (225)

2.        Goodness and being are really the same, and differ only in idea, which is clear from the following argument.  The essence of Goodness consists in this, that it is in some way desirable.  Hence the Philosopher says, Goodness is all we desire.  Now it is clear that a thing is desirable only in so far as it is perfect, for all desire their own perfection.  But everything is perfect so far as it is actual.  Therefore it is clear that a thing is perfect so far as its being; for being is the actuality of every thing, as is clear from the foregoing.  Hence it is clear that goodness and being are the same really.  But goodness expresses the aspect of desirableness, which being does not express.

3.        Now a self-mover moves itself by appetite and apprehension: since it is in them to move and not to be moved. (225)

4.        [T]he sensitive appetite is not of the good simply, but of this particular good, since also sensitive apprehension is only of the particular; and that which is good and appetible simply, is prior to that which is good and appetible here and now.   Therefore the first mover must be the appetible as an object of the understanding: and consequently the mover that desires itself must be an intelligent being.  (226)

5.        But sense is cognitive because it can receive species free from matter; and the intellect is still further cognitive because it is more separated from matter and unmixed, as is said in De Anima iii.  Since therefore God is in the highest degree of immateriality, as was stated above, it follows that He occupies the highest place in knowledge. (226)

6.        For the knowledge of an effect is sufficiently obtained from knowledge of the cause: wherefore we are said to know a thing when we know its cause.  Now God by His essence is the cause of being in other things.  Since therefore He knows His own essence most fully, we must conclude that He knows other things also. (226-7)

7.        For it has been shown that God knows other things in as much as He is their cause.  Now God's effects are singular things: because God causes things in the same way as he makes them to be actual; and universals are not subsistent but have their being only in singulars, as is proved in 7 Metaph.  Therefore God knows things other than himself not only in the universal but also in the singular. (227)

8.        Whence intellectual natures have a like disposition to good as apprehended through an intelligible form, so as to rest therein when possessed, and when not possessed to seek to possess it; both of which pertain to the will. (228)

9.        Now God wills and loves His essence for its own sake: and it cannot be increased or multiplied in itself . . . and can only be multiplied in respect of its likeness which is shared by many.  Therefore God wishes things to be multiplied because He wills and loves His essence and perfection.  (229)

10.     Therefore, from the very fact that God wills and loves Himself, it follows that He wills and loves other things. (229)

11.     The ancient philosophers . . . considered only the emanation of particular effects from particular causes, which necessarily presuppose something in their action; whence came their common opinion that nothing is made from nothing.  But this dictum has no place in the first emanation from the universal principle of things. (230n7)

12.     Whence it pertains to divine providence to produce every grade of being.  And thus for some things it has prepared necessary causes, so that they happen of necessity; for others contingent causes, that they may happen by contingency, according to the disposition of their proximate causes. (232)