Suppose the book of the elements of geometry to have been eternal, one copy having been written down from an earlier one. It is evident that even though a reason can be given for the present book out of a past one, we should never come to a full reason. What is true of the books is also true of the states of the world. If you suppose the world eternal you will suppose nothing but a succession of states and will not find in any of them a sufficient reason.

 

Key Word: Principle of Sufficient Reason

the universe and its constituent parts (no mater how small) need a total and complete reason for their existence.

Leibniz is suggesting that the universe and its constituent parts (no mater how small) need a total and complete reason for their existence, both causal and sustaining. Infinite regress is not an option so there needs to be a determinant or sufficient reason. This cannot be found in any of contingent parts of the universe.

… However far you go back to earlier states, you will never find in those states a full reason why there should be any world rather than none, and why it should be as it is. Therefore, even if you suppose the world eternal, as you will still be supposing nothing but a succession of states and will not in any of them find a sufficient reason… it is evident that the reason must be sought elsewhere.

By reason Leibniz suggests the concept of cause- in fact they could be used interchangeably. For Leibniz everything has to have an ultimate reason or cause for its beginning an continued existence and this reason is God.

For since in the series a reason cannot be found, as I have shown above, but must be sought in metaphysical necessities or eternal truths; since too, existence things cannot come into being except from existent things, as I have explained previously; it follows that eternal truths must have their existence in some subject which is absolutely or metaphysically necessary, that is in God, through whom these truths, which would otherwise be imaginary, are… realised.

Vardy and Arliss have summarized Leibniz as follows:

1. The Universe is changing.
2. Whatever is changing does not have within itself the reason for itsown existence.
3. There must be a sufficient reason for everything either within itself or outside itself.
4. Since there is no reason within the Universe for its existence, there must be a reason beyond the Universe.
5. Either this reason is itself caused or it is a complete and sufficient reason on its own.
6. There cannot be an infinite regress of causes because this will never provide a sufficient reason.
7. Therefore there must be a First Cause of the Universe which has no reason beyond itself but its own sufficient reason.
8. The first cause is God (2003:82-83).