you have rephrased it that you have begged the question and made it a premise in proving itself? By change we mean only its doing what it was not previously doing.

[The Fourth Argument]

You may be told:

We observe things coming into being, and you call this bringing what exists potentially into actuality. Thus, things coming into being must involve bringing what exists potentially into actuality. Whatever brings them into being therefore brings what exists potentially into actuality. The cause of its act of bringing them into being, which makes it bring what exists potentially into actuality, does likewise—and so on.

If, despite this, you posit a cause that brings its agency into being without bringing what exists potentially into actuality, your argument collapses.

If you hold that the First brought what exists potentially into actuality, your argument likewise collapses.

If you claim that some agents bring what exists potentially into actuality while others do not, your argument collapses. It is therefore invalid on every supposition.

This is because one of two alternatives necessarily follows from his position, and both invalidate it.

If he affirms an agent that brings what exists potentially into actuality without an external cause, the First could be such an agent, and his position is thereby invalidated.

If he does not allow an agent to bring what exists potentially into actuality except through an external cause, he must accept that the agency of every agent that brings things into being arises only through a cause that brings what exists potentially into actuality.

If the First is likewise, an impossible infinite regress follows.

If it is not, then the First brings what exists potentially into actuality without an external cause, and that invalidates his position.