According to Thrasymachus' first thesis-"Justice is the advantage of the stronger"-the only "facts" that "make" any given action "right" or "wrong" pertain to an artificial, humanly contrived system that is based upon the naked exercise of raw power.

True

Explanation:

Thrasymachus presents his views on justice in the first book of The Republic. When speaking to Socrates, Thrasymachus states that justice is not necessarily an important good, and that injustice can in fact be stronger, freer and "more masterly." Moreover, he presents three thesis:

Justice is nothing but the advantage of the stronger. Justice is obedience to laws. Justice is nothing but the advantage of another.

The first thesis states that Thrasymachus believes justice to be only a consequence of natural rights. This means that it is based on the exercise of power, and that any attempt to present an action as "just" or "unjust" would result in an artificial system that responds to these pressures of power, and not to an independent measure of justice.