Anselm & Aquinas: Proofs of the Existence of God


Doctrines & Discoveries

Notes & Quotes

The Ontological Proof

Anselm of Canterbury (1033-1109)


An a priori or ontological proof {3}

does not premise the existence or properties of the world

a posteriori or cosmological proofs argue that there are some observable properties of the world  that can only be explained (or are best explained) on the hypothesis that God DOES exist. 

a priori proofs argue from the nature of GOD ( or the definition of `God') that God MUST exist.

much like arguing from the nature of triangles (or the definition of `Triangle') that triangles must have internal angles = 180° 

My gloss of Anselm's Proof {1,2}

God =df Being than which no greater can be conceived

It's greater to really exist than just to be conceived.

God, therefore, must really exist.

1.        And so, Lord, do thou, who dost give understanding to faith, give me as far as thou knowest it to be profitable, to understand that thou art as we believe.  And, indeed, we believe thou art a being than which nothing greater can be conceived.  Or is there no such nature, since the fool hath said in his heart, there is no God? (Psalms 14: 1).  But. at any rate, this very fool when he hears of this being of which I speak -- a being than which nothing greater can be conceived -- understands what he hears, and what he understands is in his understanding; although he does not understand it to exist.  (Anselm)

2.        And assuredly that, than which nothing greater can be conceived, cannot exist in the understanding alone.  For, suppose it exists in the understanding alone: then it can be conceived to exist in reality; which is greater.  (Anselm)

3.        Therefore, if that, than which nothing greater can be conceived, can be conceived not to exist, it is not that, than which nothing greater can be conceived.  But this is an irreconcilable contradiction.  There is, then, so truly a being than which nothing greater can be conceived to exist, that it cannot even be conceived not to exist; and this being thou art, O Lord, our God. (Anselm)



Note: you can accept the conclusion as true without buying the argument (e.g.,  Anselm's Catholic critics, like Gaunilo; Theist critics of Aquinas' arguments). 


Fideist worry: with proof,  who needs faith?    

Gaunilo's parity of  reasoning objection {1}

a greatest conceivable island is conceivable

by Anselm's reasoning this island must exist

but obviously that's not necessary

Anselm's argument, consequently, is unsound

Thomist Criticism {2}

Standard (Kantian) critique

existence is not a property; perfections are: "one doesn't add anything to the nature of a nonexistent thing by bringing into existence" (Jones, p.205)

2 is false since existence is not a perfection

Doubts concerning the conceivability of greatest conceivable being (c.f. Leibniz)

RE 6: compare sphere and spheroid

RE 6 & 7: 6 seems to require that "most perfect" does mean the same when applied to God & islands

compare 5pm on the sun; round square (4)

The Ontological Proof as the image of divine self-causation

Cosmological arguments address themselves to worldly creation -- to why the world is (as it is).  Answer: God must've made it (so).  

Ontological argument addresses the question of why God (or anything) exists.  Answer: Because God's essence is to exist

Requires commitment to real preexistent (Platonic) essences? {3,5}

1.        If a man should try to prove to by such reasoning that such an island [than which no greater can be conceived] truly exists, . . . either I should believe he was jesting or I know not which I ought to regard as the greater fool: myself, supposing I should allow this proof; or him, if he should suppose that he had established with any certainty the existence of this island. (Gaunilo)

2.        Granted that everyone understands that 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)

3.        "According to Anselm we have various experiences of `degrees  of perfection' and . . . [w]e can make this judgment only because we have a standard of comparison: the idea of absolute perfection" (Jones p.203) 

4.        "Anselm could and did reply [to Gaunilo] that "most perfect" has one meaning when applied to "island," another when applied to "being" (Jones p.205) 

5.        In general the ontological argument will seem plausible to those who incline toward Platonic realism, for the realist conceives the object known (the universal) to be present in the knowing mind, illuminating it, as it were.  If this is true of even the most ordinary universal, it will obviously be even more true of God, if He is conceived of, not as a particular being, but as the most universal of universals.  By the same token, the ontological argument will seem implausible to those who tend toward nominalism. (Jones, 206)

Cosmological Proof Five Ways

a posteriori or cosmological proofs argue that some observable properties of the world can only be explained (or are best explained) on the God hypothesis. 



Thomas Aquinas





Contra 1’s  directed: Aristotelian theory of Elements & their natural motions is false. 

Contra 1’s unintelligent: panpsychism.

1+2 cuts both ways -- perhaps we should not be too quick to judge them unintelligent -- they seem to pursue ends!

Overall: unwarranted leap to one very high grade .

1st Argument: from Motion {1}

1.        Some things are in motion (as our senses show).

2.        Whatever is moved is moved by another.

3.        motion is actualization of a potential

4.        requiring prior actuality in the mover & unactualized potential in moved

5.        This cannot go on to infinity.

6.        So, there must be a first (unmoved) mover.

7.        This first mover is God.

RE2: act-pot view of cause &  non-inertial physics (Ari); RE3: perpetual cyclical motion? RE5: big leap!

2nd Arg.: from the nature of efficient cause {2}

1.        In the world there is an order of efficient causes

2.        Nothing is efficient cause of itself

3.        because then it would be "prior to itself"

4.        Efficient Causation in general involves prior actuality in the causative agent & unactualized potential in effected patient.

5.        This cannot go on to infinity.

6.        So, there must be a first mover.

7.        This first mover is God.

RE2: outdated contagion view of causation;  RE3: possibility of efficient causal cycle (& circular time);  RE5: big leap!

3rd Argument: From Possibility & Necessity {3}

1.        Some things in nature are merely possible  (contingent).

2.        Whatever is contingent is nonexistent at some time. 

3.        If everything were merely possible (contingent) then at one time there was nothing in existence.

4.        If there were ever nothing there would still be nothing -- which is absurd.

5.        Therefore there must be some necessary (eternal) being.

6.        It is impossible to go on to infinity in necessary things having their necessity caused by another.

7.        So there must be some "being having of itself its own necessity." 

8.        This is God.

RE2: Aristotelian analysis of contingency; RE3: apparent fallacy of composition -- taken separately v. all together?  Unclear the World is TEMPORARY even -- contra Aristotle -- if it IS contingent.  RE4: ex nihilo nihil fit  RE5: big leap!  RE5: illicit  extrapolation from efficient causes -- appeals to time --to derived necessities?  RE8.  Leap: some to one; the One might BE the World (a la Stoicism & Spinoza).

 4th Argument: from Gradation {4}

1.        There are gradations (of truth & goodness, as of other sorts, e.g., hotness) to be found in things.

2.        More and less -- terms of  gradation -- are predicable of things only by comparison to some maximum.

3.        There is gradation of Being.  {truer ŕ realer}

4.        The max. of a genus is the cause of all that genus.

5.        There is a truest & best thing which is the cause of else's being, goodness, & truth.

6.        This is God.

RE2: doubtful -- strongly Platonic -- principle; Corollary: RE3: Appeal to authority of Aristotle (correspondence truth underlying; good reason to deny gradations of truth IMO.  RE4: appeal to Aristotle. Adam the ideal man?  RE5: truest-and-best?  RE6: unity unargued.

5th Argument: the Governance of the World {5}

1.        Natural bodies, themselves lacking in intelligence, nevertheless act for -- are directed at -- ends.

2.        Without intelligence nothing can direct anything towards an end.

3.        So, unintelligent things cannot direct themselves.

4.        Therefore some intelligent being directs them.

5.        This is God.

1.        [S]ome things are in motion.  Now whatever is moved is moved by another, for nothing can be moved except it is in potentiality to that . . . whereas a thing moves inasmuch as it is in act.  . . .  If that by which it is moved be itself moved, then this also must needs be moved by another, and that by another again.  But this cannot go on to infinity, because then there would be no first mover, and, consequently, no other mover, seeing that the subsequent movers move only inasmuch as they are moved by the first mover . . ..   [A]nd this everyone understands to be God.  (Aquinas)

2.        In the world . . . there is an order of efficient causes.  There is no case . . . in which a thing is . . . the efficient cause of itself; for so it would be prior to itself, which is impossible.  Now in efficient causes it is not possible to go on to infinity, because in all efficient causes following in order, the first is the cause of the intermediate . . . and the intermediate . . . of the ultimate cause.  Now to take away the cause is to take away the effect.  Therefore, if there be no first cause . . . there will be no ultimate, nor any intermediate, cause.  . . .  [W]hich is plainly false.  Therefore it is necessary to admit a first efficient cause, to which everyone gives the name of God. (Aquinas)

3.        We find in nature things that are possible to be and not be, since they are found to be generated, and to be corrupted . . ..  [B]ut it is impossible for these always to exist, for that which can not-be at some time is not.  Therefore, if everything can not-be, then at one time there was nothing in existence.  . . . that which does not exist begins to exist only through something already existing.  Therefore, if at one time nothing was in existence . . . even now nothing would be in existence -- which is absurd.  Therefore . . . there must exist something the being of which is necessary.  . . .  [I]t is impossible to go on to infinity in necessary things which have their necessity caused by another, as has already been proved in regard to efficient causes.  Therefore we cannot but admit the existence of some being having of itself its own necessity . . . .  This all men speak of as God. (Aquinas)

4.        Among being there are some more and some less good, true, noble, and the like.  But more and less are predicated of different things according as they resemble . . .  something which is the maximum . . . so that there is something which is truest, something best . . . and, consequently something which is most being, for those things that are greatest in truth that are greatest in being, as is written in Metaph. ii.  Now, the maximum in any genus is the cause of all that genus, as fire, which is the maximum of heat, is the cause of all hot things, as is said in the same book.  Therefore there must be something which is to all beings the cause of their being, goodness, and every other perfection; and this we call God.  (Aquinas)

5.        [T]hings which lack knowledge, such as natural bodies, act for an end . . . acting always or nearly always in the same way, so as to obtain the best result.  Hence it is plain that they achieve their end not fortuitously but designedly.  Now whatever lacks knowledge cannot move towards an end, unless it be directed by some being endowed with knowledge and intelligence; as the arrow is directed by the archer.  Therefore some intelligent being exists by whom all natural things are directed to their end; and this being we call God. (Aquinas)