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would be more forceful if Aquinas could say that the mover must |
be actually F, but he cannot say that, at least not with perfect generality. |
For Aquinas thinks that God can move things in many ways that God is |
not actually: God can fatten a man without himself being fat. In that case, |
God is said to be virtually F, where something is β virtually F β if it is not |
itself F but it has the power to make others F. One may say, then, that |
something is in a state of actuality relevant to F when it is either actually |
F or virtually F. |
It is certain, and obvious to the senses, that in this world some things are |
moved. But everything that is moved is moved by another. For nothing is |
moved except insofar as it is in potentiality with respect to that actuality |
toward which it is moved, whereas something effects motion insofar as it is |
in actuality in a relevant respect. After all, to effect motion is just to lead |
something from potentiality into actuality. But a thing cannot be led from |
potentiality into actuality except through some being that is in actuality in a |
relevant respect; for example, something that is hot in actuality β say, a fi re |
β makes a piece of wood, which is hot in potentiality, to be hot in actuality, |
and it thereby moves and alters the piece of wood. But it is impossible for |
something to be simultaneously in potentiality and in actuality with respect |
to same thing; rather, it can be in potentiality and in actuality only with |
respect to different things. For what is hot in actuality cannot simultaneously |
be hot in potentiality; rather, it is cold in potentiality. Therefore, it is impossible |
that something should be both mover and moved in the same way and |
with respect to the same thing, or, in other words, that something should |
move itself. Therefore, everything that is moved must be moved by another. |
If, then, that by which something is moved is itself moved, then it, too, |
must be moved by another, and that other by still another. But this does not |
go on to infi nity. For if it did, then there would not be any fi rst mover and, |
as a result, none of the others would effect motion, either. For secondary |
movers effect motion only because they are being moved by a fi rst mover, just |
as a stick does not effect motion except because it is being moved by a hand. |
Therefore, one has to arrive at some fi rst mover that is not being moved by |
anything. And this is what everyone takes to be God. (ST I, q2, a3, response) |
12 Timothy J. Pawl |
P1. Some things are moved. |
P2. If something is moved to being F, then it is potentially but not actually |
F. |
P3. If something moves a thing to be F, then it (the mover) is in a state of |
actuality relevant to F. |
C1. If something were to move itself to be F (e.g., be both moved and |
its own mover), then it would be both potentially but not actually F |
and also in a state of actuality relevant to F (conjunction, and modus |
ponens , P1, P2, P3). |
P4. But it is not possible for something to be both potentially but not actually |
F and also in a state of actuality relevant to F. |
C2. It is not possible for something to move itself to be F ( modus tollens, |
C1, P4). |
P5. If it is not possible for something to move itself to be F, then if something |
is moved, it is moved by something else. |
C3. If something is moved, it is moved by something else ( modus ponens , |
C2, P5). |
P5. If B moves A and B is moved, then B must be moved by some other |
thing, C. And if C is moved, then C must be moved by still some other |
thing, D. And so on. |
P6. If the series of movers were to go on to infi nity, then there would be |
no fi rst mover. |
P7. If there were no fi rst mover, then there would be no motion. |
C4. There is a fi rst mover ( modus tollens , P1, P7). |
C5. That fi rst mover is the thing that everyone takes to be God |
(defi nition). |
The Second Way β The Argument from Causation |
Whereas the First Way focused on accidental changes, the Second Way |
focuses on ordered series of effi cient causation. An effi cient cause is that |
which produces something or an alteration in something. The composer is |
the effi cient cause of the sonata; the fi re is the effi cient cause of the heating |
of the kettle. An ordered series is a series in which the causal work of later |
members in the series depends on the simultaneous causal work of earlier |
members in the series. If the fi re heats the kettle and the kettle heats the |
water, it is an ordered series, since the kettle β s heating the water depends |
upon the causal activity of the earlier cause, the fi re. Likewise, a system of |
gears is an ordered causal series, since the causal action of one intermediate |
gear spinning another, later gear depends upon the causal activity of previous |
gears in the system. Aquinas argues in the Second Way, to continue |
with the gear image, that the system cannot be gears all the way back. An |
Aquinasβ Five Ways 13 |
infi nite series of gears, without a fi rst cause of their spinning, would not be |
in motion. |
We fi nd that among sensible things there is an ordering of effi cient causes, |
and yet we do not fi nd β nor is it possible to fi nd β anything that is an effi cient |
cause of its own self. For if something were an effi cient cause of itself, then |
it would be prior to itself β which is impossible. |
But it is impossible to go on to infi nity among effi cient causes. For in every |
case of ordered effi cient causes, the fi rst is a cause of the intermediate and the |
intermediate is a cause of the last β and this regardless of whether the intermediate |
is constituted by many causes or by just one. But when a cause is |
removed, its effect is removed. Therefore, if there were no fi rst among the |
effi cient causes, then neither would there be a last or an intermediate. But if |
the effi cient causes went on to infi nity, there would not be a fi rst effi cient |
cause, and so there would not be a last effect or any intermediate effi cient |
causes, either β which is obviously false. Therefore, one must posit some fi rst |
effi cient cause β which everyone calls God. (ST I, q2, a3, response) |
P1. There is an ordered series of effi cient causes. |
P2. Necessarily, if X is an effi cient cause of Y, then X is prior to Y. |
C1. Necessarily, if X is an effi cient cause of X, then X is prior to X |
(instantiation, P2). |
P3. It is not possible for X to be prior to X. |
C2. It is not possible for X to be an effi cient cause of itself ( modus tollens , |
C1, P3). |
P4. If something is an ordered series of effi cient causes, then the fi rst cause |
causes the intermediate cause(s), and the intermediate cause(s) cause(s) |