Philosophy 1600 - Honors Seminar

 

Topic 2: Cosmological Arguments for the Existence of God

Aquinas's "Argument from Motion"

1.The Central Argument

 

(1)  Some things in this world are in motion.

(2)  Whatever is in motion is moved by something else.

(3)  Therefore the world must contain something that moves other things.  #[From (1) and (2).]

(4)  This something else, if it too is in motion, must itself be moved by something else, and that in turn by yet another thing.

(5)  But this cannot go on forever.

(6)  Therefore there must be something that moves other things but which is not itself moved by anything - that is, there must be a first, or unmoved, mover.  {From (3) and (5).]

(7)  A first, or unmoved mover is what is meant by the term 'God'.

(8)  Therefore God must exist.  [From (6) and (7).]

 
2. Sub-Argument: An Argument for Statement 2 in the Main Argument

(1)  It is a general metaphysical truth that a thing cannot change from potentiality to actuality except through the action of something which is itself in actuality.

(2)  Consider now the case of motion.  One thing that is true about motion is that nothing is in motion except in so far as it is initially in potentiality to the term of its motion, and then later in actuality with respect to that term.

(3)  Hence a thing cannot be in motion unless it is moved by something which is itself in the relevant state of actuality.  [From (1) and (2).]

(4)  It is also a general metaphysical truth that it is not possible for the same thing to be, at the same time and in the same respect, in actuality and potentiality.

(5)  So it is impossible that in the same respect and in the same manner anything should be both mover and moved, or that it should move itself. [From (3) and (4).]

(6)  So whatever is in motion must be moved by something else. [From (3) and (5).]