A Failed Argument for PSR

In Saint Thomas and the Principle of Sufficient Reason Scott Sullivan claims denial of PSR entails a contradiction.

Sullivan works with the usual Thomistic formulation: everything which exists has that whereby it exists (call that an act of existence) either through itself or from another.

From there, Sullivan claims denial of the first conjunct commits someone to saying something both does and does not have that which distinguishes it from nothing = a contradiction. Let that be granted.

However, Sullivan then claims the second conjunct, which he calls the Source Portion (“either through itself or from another”), also cannot be denied without contradiction.

Unfortunately, this is question begging against the brute fact skeptic, despite what Sullivan later tries to argue concerning the nature of petitio principii. To say something has that whereby it exists either from itself or through another assumes brute facts are not available (i.e., neither through itself or from another: it just has it!).

Of course, I believe the position of the brute fact skeptic is rationally untenable, but I cannot side with Sullivan in saying it entails a contradiction. So, while I commend his book for its many other ludic defenses of PSR, it seems his boldest contribution fails.