Aristotle's criticism of Platonic Forms in the Metaphysics has been a major source for the understanding and developments of the theory of Forms in later Antiquity. One of the cases in point is Aristotle's argument, in Metaphysics I 9, 990b22-991a2, against Forms of non-substances. In this paper, I will first provide a careful analysis of this passage. Next, I will discuss how the argument has been interpreted - and refuted - by the fifth-century Neoplatonists Syrianus and Proclus. This interpretation has (...) played an important role in the broader context of the Neoplatonic debates on the range of Plato's theory of Forms, which was one of the traditional problems discussed about the Forms in later Platonism. (shrink)