  The construction of first-order logic and set theory gives rise to apparent
circularities of mutual dependence, making it unclear which can act as a
self-contained starting point in the foundation of mathematics. In this paper,
we carry out a metatheoretic and finitistic development of a first-order
logical system in which we define formal set theory (ZFC). We contend that the
techniques employed in constructing this system offer a philosophically sound
basis for introducing ZFC and proceeding with the conventional formal
development of mathematics. Lastly, by examining the chronology of the
aforementioned construction, we attempt to answer the titular question.
