The Argument from Motion in the Summa Contra Gentiles: Everything Moved Is Moved by Another

Orientation #

He begins “here at chapter thirteen” of the Contra Gentiles, and says he is “not going to go into” the preceding chapters (God’s existence not obvious; not undemonstrable) except briefly. He refers back to “when we talked about nature” and “when we were showing that nature acts for an end” (earlier classes, not resolved by the context block). He says an objection from Avicenna comes next, and that the mover’s complete immobility is “developed more fully later on.” The previous class compared the arguments from motion in the two Summae; the next continues with Thomas’s treatment of the regress arguments.

The class, in order #

1. Before demonstrating: two positions Thomas rejects (“those two positions that Thomas rejects”) #

Point: in both Summae Thomas first asks whether God’s existence is obvious, then whether it can be demonstrated; the two views he rejects are extremes.

• Error 1: the existence of God is obvious (though, as said before, there are “some evident signs of him” even to the average person).
• Error 2: it cannot be demonstrated.
• Parallel from Aristotle on nature: after investigating what nature is, Aristotle says it would be “laughable” to demonstrate that nature exists. Such a man could not distinguish what is known by itself from what is known by another; he “thinks he doesn’t know, but in fact he does know.”
• This is the reverse of the condition Socrates exposed (thinking you know what you don’t); Heraclitus said the same before him (“men do not understand the things they meet every day, although they think they do”).
• Argument that the reverse condition is possible:
  1. A man can mistake the unknown for the known, because he sometimes cannot distinguish the two (well known from Socrates).
  2. If you cannot distinguish two things, you can make the mistake in either direction.
  3. So one can mistake the known for the unknown.
  • Examples for premise 2: if one can take Michael Jackson (a man, “benefit of the doubt”) for a woman, one can take some woman for a man; orange for apple and the reverse; Budweiser for Miller and the reverse; a guest who took peach-flavored wine for Earl Grey (he plans to serve Earl Grey next time as “peach wine”).
• Why trying to prove the obvious is laughable: you would prove it by what is less obvious, “the unknown before the known.”
• The truth lies between the extremes: neither obvious nor unknowable, but knowable by demonstration—demonstration quia (effect to cause), not propter quid (cause to effect); both kinds taught in the Posterior Analytics, so Thomas refers back to logic.

2. The Church, Paul, Goethe, and a student’s question (“the First Vatican Council”) #

• Vatican I said God’s existence can be demonstrated, citing Paul; Romans 1:20 (“the invisible things of God … made known through the visible things”), the “key text,” authoritatively defined. He mentions this because people “even in Catholic colleges” now deny it—“always making the old mistakes.”
• Goethe’s image (quoted before): the wise man swims up the river separating true from false; as he goes on they come back together—“the whole description of history.” Thomas separates truth from the two falsehoods; then everyone comes back together in the same mistakes.
• Student: how does “God’s existence is obvious” differ from “naturally known in some way”? Answer: “a hard thing to do”; that is why he says the Greeks “thought” there was a God with providence—their notion of what God is may be hazy, “a kind of imperfect knowledge.” Example: his mother as a little girl—God can hold the universe with his little finger; even believers have only a hazy notion of God.

3. Why truth explains the errors: Trinity and Incarnation (“the truth is in between two extremes”) #

Point: if the whole truth were one extreme, no one would think the other; the truth in the middle explains both errors, because “men err because they see some part of the truth, but not the whole truth” (Empedocles: they “boast of having seen the whole”).

• Trinity: truth is one nature, three persons. Sabellius: one nature, so one person. Arius: three persons, so three natures. If the truth were one/one, there would be no basis for thinking three/three, and vice versa; but each heresy holds a real part of the truth and is misled by it.
• Incarnation: reversed—one person, two natures. Monophysites: one person, so one nature. Nestorius: two natures, so two persons (hence he said Mary should not be called Mother of God). Neither extreme explains how the other could arise; the true middle explains both.
• Application: “so knowable it needn’t be demonstrated” has the truth that God is known in some way; “not knowable, just a matter of belief” has the truth that it is not obvious or perfectly known. “Truth often lies in the middle.”

4. Demonstrations or “converging probabilities”? (“converging probabilities”) #

Student: some (he recalls the Catechism’s wording, but has not the text) say Thomas gives converging probabilities, not demonstrations. Berquist: the fundamental text is Vatican I, which the Catechism refers back to. His answer by analogy to showing nature acts for an end:

• Aristotle’s first argument: nature produces the good in the parts and order of animals and plants almost always; by chance, that would happen rarely. This stands by itself.
• Second argument: nature starts from a definite beginning (seed, fertilized egg) and goes through an ordered number of steps resulting in the good animal or plant; that too is contrary to chance. Compared to art: follow the meringue pie recipe and you get a meringue pie, not chocolate cream.
• Separate arguments, each valid alone, but “the two of them together are even stronger.” So several demonstrations are not “opposed” to being demonstrations.

5. Reading the first way (“everything that is moved or is in motion”) #

Text: having shown it is not vain, Thomas lays down the reasons by which “both the philosophers as well as the Catholic teachers” prove God to be; first Aristotle’s, who proves it from motion “in two ways” (duobus viis). Hence “five ways”—roads; “all roads lead to Rome,” all these lead to God.

• The argument as he reads it:
  1. Everything that is moved is moved by another.
  2. It is clear by the senses that something is moved, e.g. the sun.
  3. So the sun is moved by another. Either that mover is moved or not.
  4. If not: an unmoved mover, “and this is what we call God.”
  5. If it is moved: either this goes on forever, or one comes to an unmoved mover; but it cannot go on forever. So one must posit a first mover that is itself immobile.
• “You’ve got to understand this in a very precise way”: “moved” means moving another insofar as it is itself being moved—like the glass pushing the paper by being pushed—not a series like father generating son generating grandson (he did not generate his son while being generated by his father). Thomas is “not attempting to exclude” an unending series of fathers; “a lot of people misunderstand that.”
• Nor does “one cannot go on forever” reject infinite series as such: a line is divisible forever, and dividing yields ever-larger numbers (one, then two, then three …), so number can increase forever—the potential infinity Aristotle and Thomas both admit. What is denied is this series: every mover a moved mover, another before each, “all at the same time”—an infinity of movers needed to move anything (“tell that to the movers” who transport furniture).
• Student on translation: movens immobile—“unmoved” or “unmoving” mover? Answer: at first what is meant is a mover that moves without being moved itself; that it is completely free of any change is “made more explicit as you go on,” especially in the Summa’s treatment of God’s substance. One need not yet have “a full understanding of the immobility of the first mover.”
• Recap: the premise that things are in motion is obvious to sense (contrary to Parmenides) and needs no proof; accept the other premises and you are “forced to the conclusion.” But two premises need backing up.
• Aside: five has always been his “Pythagorean number” (Duane has five letters).

6. The form of the argument, and where the difficulty lies (“the chief difficulty is in the matter”) #

Student found the syllogistic form hard, since it is an either/or. Answer: there is more than one syllogism.

• Order: (a) what is in motion is moved by something; (b) that mover is either unmoved or moved—exhaustive; (c) if unmoved, the conclusion is already granted; (d) if moved, either it goes on forever or comes to an unmoved mover; the first is excluded; so in either case, an unmoved mover.
• Formal logic is “not the chief difficulty in reasoning.” The rules of the if-then argument (affirm the antecedent, or deny the consequent; not the reverse) can be learned easily; the chief difficulty is the matter—whether statements are true, necessary, probable.
• Illustration, Euclid I.6 (converse of I.5: equal angles, then equal sides). Main syllogism is a simple either/or: the sides are equal or unequal; they cannot be unequal; therefore equal. “The real heart” is showing they cannot be unequal: cut off from the longer side a line equal to the shorter (earlier theorem), draw the line; the two triangles have an equal angle contained by equal sides (one side by construction, one common), so by I.4 they are equal—a regular syllogism, “what Aristotle called a syllogism period.” But that is absurd: the part equal to the whole, “the lesser to the greater, as Euclid says.” That backs up the if-then: if unequal, then part equals whole. The main syllogism is formally closer to the conclusion but not where the difficulty is.
• Applied here: “either the mover is unmoved or moved”—take the first and you grant the conclusion; the work is in the other branch, and in backing up the premises.

7. Two propositions to be proved; “the Philosopher” and figures of speech (“proves in what three ways”) #

• Text: two propositions need proof—everything moved is moved by another; and in movers and moved one cannot go on forever. In the Summa Theologiae he gives one reason for each; here, three ways for each. “The Philosopher proves the first in three ways.”
• Who is “the Philosopher”? Plato’s star student (not Aristotle’s). Calling him “the Philosopher” (capitalized in English, which has the article) is antonomasia.
• Antonomasia vs. synecdoche: both give the name of a whole to a part or vice versa, but antonomasia is based on the universal whole and its part, synecdoche on the composed whole and its part.
  • Synecdoche: “the Word was made flesh”—flesh for man; our word “incarnation” comes from it. Arius (he thinks) misread it: the Logos in place of a soul. Scripture calls us “souls” or “flesh” (“to you all flesh must come”); “he’s a brain,” “she’s all heart,” his brother Mark marrying: “going the way of all flesh”—the part stands out.
  • Antonomasia: indicates the excellence of one particular under the general—the White House; Christ; the Bible (“the book”); a Hamlet for one who hesitates; a Romeo, Don Juan, Casanova; Thomas calls Paul “the Apostle” (Peter and Paul, coupled in Rome’s churches; he was married on their feast, June 29); the Gospels, “the good news”; the Apocalypse, the revelation; Isaiah’s names for Christ; “miracle,” filled with wonder.
  • Student: is “sacred page” for the Bible synecdoche? Yes—page of the book; whereas sacra scriptura names by antonomasia (the saints’ writings are sacred too in some way).
• We use these figures daily without knowing their names.
• Aside: news on the drive up—a priest shot by someone he had abused; “it goes on and on.”

8. First proof that whatever is moved is moved by another (“based on the what? Sixth book”) #

Point: Aristotle’s first proof rests on Physics VI (the divisibility of what is moved); Aristotle begins developing it at the start of book VII, later going back to book III and the definition of motion. This is motion in the strict sense, not “change” as of the mind.

• Three things supposed of a self-mover:
  1. It must have in itself the source of its own motion; otherwise “manifestly” it is moved by another (obvious).
  2. It must be the first moved—“more difficult.” Why? What is responsible for something’s belonging to it must have it first; if not first, it would be because of a part or something else. Student example: does being reasonable belong first to the emotions? No. So it is moved by reason of itself, not of a part—as the animal is moved by the motion of the foot; then not the whole but the part is moved by itself, and one part by another.
  3. It must be divisible, have parts—everything moved is divisible, proved in Physics VI.
• The argument:
  1. What is laid down as moved by itself is first moved.
  2. On the rest of one of its parts follows the rest of the whole (if one part rested while another moved, the whole would not be first moved, but the part).
  3. Nothing that is at rest when another is at rest is moved by itself; for that whose rest follows on another’s rest, its motion follows on another’s motion.
  4. So what was laid down as moved by itself is not moved by itself; therefore everything moved is moved by another.
• Coming next: an objection from Avicenna.
• His addition from Thomas’s commentary at the start of Physics VII: motion can never belong first to a thing in many ways, not only because the mover is divisible (motion of the whole depends on the motion of the part). When is a thing first in motion? What is the first distance it goes, the first time? “There’s no first”—recalling that before any motion you have already moved some distance. If motion cannot belong first to anything, and what one is responsible for must belong to it first, one cannot be responsible for one’s own motion. Student: those are different senses of “first”—granted, “but it seems to add something.” Student: the self-mover would be both agent and patient—“that’s going to come up later.” Thomas’s text here is “kind of a summary” of the eight books of Natural Hearing.
• The class breaks off mid-sentence: “So it seems that the places …”

His words #

• known by itself vs. known by another: the distinction the man who demonstrates nature’s existence cannot make.
• demonstration quia vs. propter quid: from effect to cause vs. from cause to effect; God’s existence known by the former.
• “five ways”: roads; all lead to God.
• moved by another: moving another insofar as itself being moved by another, at the same time (glass pushing paper).
• unmoved / unmoving mover: his rendering of movens immobile; first, a mover not moving through being moved; full immobility later.
• potential infinity: “infinity and the limit”; the divisible line, number increasing forever—not what the argument denies.
• the matter of an argument: truth, necessity, probability of the statements, as against form.
• “syllogism period”: Aristotle’s plain categorical syllogism (the I.4 step).
• antonomasia: name of the universal given to a particular (or vice versa), often for its excellence.
• synecdoche: part for the composed whole (“flesh” for man).
• Natural Hearing [ed.: Physics].
• first moved: what moves itself must be moved by reason of itself, not of a part.

Texts #

Read in class:

• Thomas Aquinas, Summa Contra Gentiles I, ch. 13 (opening; first way from motion; the two propositions to be proved; Aristotle’s first proof, from Physics VI) Mentioned:
• Summa Theologiae (one reason for each proposition; God’s complete immobility explicit in treating his substance)
• Aristotle, Physics II (laughable to prove nature exists; nature acts for an end) (inferred); Physics VI (everything moved is divisible), VII (start of the argument; Thomas’s commentary: no first in motion), III (definition of motion)
• Aristotle, Posterior Analytics (quia / propter quid)
• Plato/Socrates; Heraclitus; Empedocles (“boast of having seen the whole”); Parmenides
• Vatican I; Romans 1:20; the Catechism (student)
• Euclid, Elements I.6, with I.5 and I.4
• Goethe (wise man swimming up the river)
• John 1:14 (“the Word was made flesh”) (inferred); Isaiah’s names for Christ

His questions #

• Why is it laughable to try to demonstrate that nature exists? Because it is obvious; you would prove the known by the less known.
• Could you know something and not know that you know it? Yes—if one can confuse two things in one direction, one can in the reverse.
• If God’s existence were obvious, why would anyone think it unknowable (and vice versa)? They wouldn’t; the truth in the middle explains both errors, as with the Trinity and Incarnation.
• Is it clear by the senses that something is moved? Yes, e.g. the sun—contrary to Parmenides; no proof needed.
• Is Thomas rejecting an infinite series as such (fathers going back forever; the line divisible forever)? No; only a series of moved movers all moving at the same time.
• Where is the chief difficulty in reasoning—form or matter? Matter; the form (as in Euclid I.6’s either/or) is easy.
• Who is “the Philosopher,” and what figure of speech is that? Plato’s star student, Aristotle; antonomasia.
• Why must what moves itself be the first moved? What is responsible for something’s belonging to it must have it first, not through a part.
• When is something first in motion? What is the first distance? There is no first—so motion cannot belong first to anything.
• Would the self-mover be both agent and patient? Left open—“that’s going to come up later.”