1. There is causal activity in the world.
2. Nothing is the cause of itself. (Everything has a cause or some things have no cause.)
(i) In order of causes A (the first) is the cause of the second, B, and B is the cause of C (the ultimate cause or the present moment.)
(ii) To take away the cause is to take away the effect, i.e., take away A and you take away B which in turn eliminates C - that is, all of US!
(iii) To go on to infinity is to take away the first cause, A, which would take away C and B.
(iv) But C, present causal activity - us and the universe - do exist, so
______________________________
3. Going on to infinity in the order of causes is impossible.
___________________________________________
4. Therefore, there must be a First Cause
5. This First Cause is what everyone calls God.
Aquinas's argument: Analysis
The argument seems to be this:
Let us take some causal series and refer to its member by the letters of the alphabet:
A---- B---- M---- N------ Y----- Z.
Z stands for something presently existing. If A had never existed none of the subsequent members of the series would have come into existence. But it is precisely A that the believer in the infinite series is "taking away." For in maintaining that the series is infinite he is denying that it has a first member; he is denying that there is such a thing as a first cause; he is, in other words, denying the existence of A. Without A, Z could not have existed, but this is plainly false.
The critics reply:
Aquinas has failed to distinguish between two statements:
1. A did not exist.
2. A is not uncaused.
To say that the series is infinite implies 2, but it does not imply 1. If everything is caused then so is A; thus the existence of A is not being denied, merely its claim to be the FIRST. If you tell me that you are the Greatest Person Who Ever Lived, and I say, "No you aren't" I am not denying your existence, I am just denying you that title. Thus, a believer in infinite series is not denying the status of existence to any of its members, she is merely denying that any ONE cause can claim to be FIRST.
Other problems with the argument. Why couldn't there be a multiple number of first causes - a magnetic field of subatomic particles? If you ask, what is the cause of these, the answer could be: "Nothing, some things have no causes." You admit that God has no cause, so why couldn't the most basic constituents of matter have no causes?
Now, some versions of the argument use the premise that something can't come from nothing, therefore God must have created the Universe. But, if God created the Universe, what did he create it out of ? - Nothing? In addition, this still wouldn't answer the question,"Why this particular Universe?" "Why not one which is better?" Or, "Why did God create a universe at all?" There are lots more "Why questions" which could be asked. The real problem for the sceptic is that a"a god" doesn't seem to explain much. By the way, I am not insisting that the Universe has an infinite history, I am merely saying that it could. It may well be that there was a first instant, for example, a Big Bang. Perhaps God even caused the Big Bang, but it wouldn't explain very much.