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The Principle of Sufficient ReasonGottfried Wilhelm Leibniz (1646-1716) avoided the problem of infinite regression by reinterpreting the endless series, not of events, but of explanations. Even if the universe had always existed, there was nothing within the universe to show why it exists. According to Leibniz, everything has a sufficient reason.
The Principle of Sufficient Reason states that, in the case of any positive truth, there is some reason for it, i.e. there is some sort of explanation, known or unknown, for everything. The world does not seem to contain within itself the reason for its own existence. Therefore God exists.
Leibniz, in his Theodicy (written in 1710) put the Cosmological Argument forwards as follows:
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, 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.
Leibniz says that ‘the great principle’ of the Cosmological Argument is that ‘nothing takes place without a sufficient reason’. This is known as the Principle of Sufficient Reason. By a ‘sufficient reason’ Leibniz means a complete explanation. Thus to explain the existence of one book by saying that it is copied from another or to explain your existence by saying that you were a child of your parents only gives a partial explanation. If there is going to be a complete or sufficient reason for the book or for your existence, we have to get back to something that does not depend on anything else – and this will be God.
Leibniz is saying that if we suppose the world to be everlasting – to go on and on, backwards in time for ever – we will never come to a complete or sufficient explanation for its existence. We should not be satisfied with such an unending regress, he claims, but should instead recognise that the whole universe depends on God, who is uncaused and does not depend on anything else.
The question is, of course, whether we have to accept the Principle of Sufficient Reason. Is it any more improbable that each state of the universe should be explainable by a previous state – going on and on to infinity – than that the universe should depend on an uncaused God? Scientists do now know that if we go back in time to the very beginning of the universe, time ceases to exist at the moment of the ‘Big Bang’. The universe and time itself started with the Big Bang. This, perhaps, may make it less plausible to claim that each state of the universe can be explained by a preceding state. If, as critics of the Cosmological Argument claim, God was not the cause of the Big Bang, they need to suggest what the cause was.