 Theophrastus’ short treatise Metaphysics or On First Principles is an inquiry into the foundations of natural science; it studies the first principles of nature as well as their relationship to the world of perceptible and changeable entities. It is recognized by scholars as an integral and independent work, which was most probably written during Theophrastus’ stay in Assos or, at the latest, at the very beginning of Aristotle’s final stay in Athens; that is to say, in the period between 347 and 334 BCE. The early date of the composition of this treatise has been argued mainly on the basis of the following two considerations: (i) Theophrastus seems to have known nothing of the central and latest books of Aristotle’s Metaphysics, and thus concentrated all his comments on the older books, and especially on book Lambda. (ii) Some of the puzzles raised by Theophrastus in this treatise are resolved in Aristotle’s works On the Parts of Animals and On the Generation of Animals; had the Aristotelian works been available to him, he would not have made these remarks (see Most 1988; Devereux 1988; Huby 2015).