Aquinas on the eternity of the world

The XIII century saw a big controversy on whether it could be proved, and not merely accepted by faith, that the world began. 

1. All the classical Greek and Roman philosophers were in agreement that the world is eternal in the sense that it has always existed and will always exist. Aquinas, like all orthodox Christian philosophers disagreed because scripture teaches us otherwise. Hence, he set out to show that the arguments for the eternity of the world are inconclusive. Here are a few of them.

So, it cannot be proved that the world is eternal. However, this leaves open the issue of whether it can be proved that the world is not eternal. For example, Saint Bonaventure held that it can be proved that the world began. Saint Thomas Aquinas disagreed. Here we look at some of the arguments of Saint Thomas.
2. Since Aquinas adopted the Aristotelean theory of demonstration, according to which science deals with what is necessary (that which cannot be otherwise), he held that it's impossible to prove that the world began because:

3. Aquinas considers eight objections to his view (that is, eight arguments allegedly proving that the world is not eternal, i.e., that the world began), and answers them.  Here we'll look only at five:

  1. One can prove that the world is caused (created) by God. But an effect must have a beginning in time, and therefore the world is not eternal.

    Reply: God's act of creation is not successive but instantaneous, and an effect of an instantaneous act need not have a beginning. Augustine's example of the eternal foot imprint which is eternal because its maker (the fooot) is also eternal.

  2. Nothing can be equal to God in any respect.  But if the world had no beginning, it would be equal to God with respect to infinite duration.  Hence, the world has a beginning.
    Reply: Divine duration is not successive. (This ivolves the distinction between eternity proper and sempiternity).
  3. If an infinity of days had to pass before today, then today would never had arrived because it's impossible to traverse the infinite.
    Reply: this presupposes a starting day by adding to which we get to today. But there is no such starting day, and from any day in the past one can get to the present one in a finite number of steps.
  4. If the world were eternal, then any man would have been begotten of a previous one in an infinite series.  But the father is the efficient cause of the son, and an infinity of efficient causes is impossible.

    Reply: Aquinas draws a distinction between two types of series of efficient causes:

  5.  

  6. If the world were eternal, then there would be an infinity of souls of human beings. But no infinite number of anything can exists.

    Reply: One could reply that the soul dies with the body, or appeal to reincarnation, or deny that human souls always existed.