Several of Thomas Aquinas's proofs for the existence of God rely on the claim that causal series cannot proceed in infinitum. I argue that Aquinas has good reason to hold this claim given his conception of causation. Because he holds that effects are ontologically dependent on their causes, he holds that the relevant causal series are wholly derivative: the later members of such series serve as causes only insofar as they have been caused by and are effects of the earlier (...) members. Because the intermediate causes in such series possess causal powers only by deriving them from all the preceding causes, they need a first and non-derivative cause to serve as the source of their causal powers. (shrink)

The article analyzes the status of metaphysics in relation to other sciences, especially the sense and reasons behind its priority in the system of sciences, as conveyed in the works of Thomas Aquinas. The question of what comes first in the system of sciences has led to an exploration and justification of the criteria behind this priority. According to Thomas Aquinas, metaphysics is justly considered to be the first philosophy: on the one hand it is occupied with what comes first (...) in the ontological order – the first causes of being, on the other hand, other sciences rely on it for their first principles. The article critically analyzes both substantiations of the idea of being first. The substantive criterion is questioned by the introduction of revealed theology into the system of sciences accepted by Aquinas; revealed theology is also occupied with what comes first, and does so with greater authority than metaphysics. The article focuses on the analysis of main doubts concerning metaphysics’ methodological criterion of priority: the idea that metaphysics, in relation to other sciences, is in a sense first and functions as a determinant, while also being last and determined by these very sciences. Metaphysics is first, as other sciences draw from it their first principles, and last, as it utilizes facts established by other sciences which come first in the process of knowledge acquisition. Hence the charge that Aquinas’ argumentation concerning metaphysics’ priority is circular in nature. The article analyzes various aspects of this difficulty and offers suggestions on how to overcome them. (shrink)