The following is an interpretation of Aquinas’ agent intellect focusing on Summa Theologiae I, qq. 75-89, and proposing that the agent intellect is a metaphysical rather than a formal a priori of human understanding. A formal a priori is responsible for the intelligibility as content of the object of human understanding and is related to Kant’s epistemological views; whereas a metaphysical a priori is responsible for intelligibility as mode of being of this same object. We can find in Aquinas’ text (...) many indications that the agent intellect is not productive of the universal as content but is, rather, productive of the abstracted or intelligible mode of being of the universal nature. This is because for Aquinas the universal nature, which is the object of human understanding, is present in the things themselves but with a different mode of being. Chapter 1 is intended to establish the fact which requires for Aquinas an agent intellect, and provides two very important principles: one is that the object of human understanding (the universal nature) is present in the things themselves and, the other, that it is not in the things themselves with a mode of being which makes it available to the intellectual eye. These two principles lead us to the main point of Chapter 2, namely the distinction between the intelligible object and its intelligible mode of being. Now, because knowing is receptive of the intelligible object (Chapter 3), which is present in the things themselves (Chapter 1), the agent intellect is productive not of the object’s intelligible content, but of its abstracted or intelligible mode of being (Chapter 4). (shrink)