Theophrastus' so-called Metaphysics presents a series of difficulties for various accounts of first principles, including Platonist ones but also – and especially – Aristotle's. Hence, many scholars think that Theophrastus abandons some of his teacher's core commitments, such as the prime mover or natural teleology. Other interpreters, by contrast, emphasize the aporematic character of the work and do not take Theophrastus to be truly critical of Aristotle. In the author's view, neither reading captures the character of the treatise. For, as argued in this Element, Theophrastus probes the Aristotelian account of first principles in earnest. But this is not to say that he abandons it. Rather, Theophrastus is an internal critic of an Aristotelian framework to which he himself is committed but of which he thinks that it requires further elaboration.