Way is often called the argument from efficient causes, and Aquinas argues:
1) There is an "order of efficient causes" in the universe.
2) Nothing can be the cause of itself because that would entail its being prior to itself which is impossible.
3) Therefore, all things must be caused by things other than themselves.
4) There cannot be an infinite series of efficient causes stretching backwards.
5) To take away the cause is to take away the effect.
6) If there is no first cause, there can be no intermediate causes and therefore no effects, "all o
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