3 Second Way
The second way is from the nature of the efficient cause. In the world of sense we find there is an
order of efficient causes. There is no case known (neither is it, indeed, possible) in which a thing
is found to be the efficient cause of itself; for so it would be prior to itself, which is impossible.
Now in efficient causes it is not possible to go on to infinity, because in all efficient causes
following in order, the first is the cause of the intermediate cause, and the intermediate is the cause
of the ultimate cause, whether the intermediate cause be several, or one only. Now to take away
the cause is to take away the effect. Therefore, if there is to be no first cause among efficient
causes, there will be no ultimate, nor any intermediate cause. But if in intermediate causes is
possible to go on to infinity, there will be no first efficient cause, neither will be there an ultimate
effect, nor any intermediate efficient causes; all of which is plainly false. Therefore it is necessary
to admit a first efficient cause, to which everyone gives the name of God.
The Second Way is “similar” to the First Way, “but rather than focusing on motion, it focuses on efficient causation.” Peter Kreeft states, “Efficient cause for Aristotle meant only cause of change, cause of form informing matter. But for St. Thomas it means also the cause of the very existence of the effect.” Kreeft thinks that the second way “goes beyond the first: the first proved God as the cause of universal change; the second proves God as cause of the very existence of the universe.” The First Way pointed how that the existence of change was obvious to everyone. Second, Aquinas concludes that a first mover was the cause of motion. In the second way, he argues that for intermediate causes to exist, there must be a “first efficient cause.”
In the Second Way, people find the existence of efficient causes in the world and that they are “ordered in a series.” Aquinas agreed with Aristotle’s assertion that there are four causes: material, formal, efficient, and final. Davies states, “But, in addition to material, formal, and final causes, there are, according to Aquinas, ‘efficient causes,’ which he thinks of as what we appeal to when we offer explanations in terms of the activity of something (or of many things). With efficient causation, the focus, for Aquinas falls on questions of the form ‘What did that?’, or keeps that going’?” So, efficient causes cause certain effects. Aquinas argues that no efficient cause can be the cause of itself. Aquinas concludes that a first cause is needed to explain the existence of intermediate causes and this first cause is God.