 It is worth considering why Plutarch engaged in writing so many polemical works against the two main Hellenistic schools of philosophy.  One reason for Plutarch's preoccupation must be that the early Stoics and Epicureans both strongly criticized Plato. The Epicurean Colotes, for instance, Plutarch's target in the Against Colotes, was critical of Plato's dialogues in his Against Plato's Lysis and Against Plato's Euthydemus (meager fragments of which are preserved in Herculaneum papyri PHerc. 208, PHerc. 1032), while he also criticized the Republic's myth of Er and the implied view of an immortal human soul (Proclus, In Rempublicam 2.109.11–12, 111.6–17; see Kechagia 2011, 53–132).  Another reason for Plutarch's engagement was the fact that both Epicureans and Stoics drew freely and extensively for their own purposes on Plato without acknowledging it and despite their criticism of Plato. This holds true especially for the Stoics (see Babut 1969a). They were inspired by the Timaeus, for instance, in their adoption of two principles, god and matter, but their god, unlike that of Plato, is immanent in the physical world and bodily, and he alone, without the Forms, suffices for the formation of matter. The Stoics were probably guided to their view that only bodies exist by passages in the Sophist (246a-247c) and in the Timaeus (31b-32c, 49d-e, 53b-c). For Plutarch, though, this is an utterly mistaken reading of the Timaeus (De communibus notitiis 1073D-1074E). Plutarch's polemics were, then, motivated by his desire to advocate Platonism against what he regarded as misguided interpretations and criticisms on the part of Epicureans and Stoics. This defense of Platonism was of vital importance for Platonism at Plutarch's time, since both Stoicism and Epicureanism were still thriving, mainly in virtue of their ethics. Plutarch wanted to show that Stoic and Epicurean ethics rest on mistaken assumptions about human nature and reality, which render their ethical doctrines useless (De virtute morali, De Stoicorum repugnantiis 1041E-1043A, De communibus notitiis 1060B-1073D). Plutarch's polemics were fuelled by the view he shares with Hellenistic philosophers that the end of philosophy is to support ethical life (see e.g. De profectibus in virtute); if a school's ethical ideal is unrealizable or, worse, unworthy of human nature, this for Plutarch (as for Antiochus, Cicero, De finibus 5.13, 5.89) is evidence that the entire philosophical system is a failure. As in the rest of his philosophical works, in his polemical treatises too, Plutarch aims to show that Plato's philosophy makes good sense as a whole, that is, it does justice to the world and human nature and can bring human beings to happiness (see below, sect. 2), but in his polemical works Plutarch aims especially to demonstrate that departure from Plato results in self-contradictions, of which he accuses the Stoics in particular (Boys-Stones 1997a). Two further features of Stoic and Epicurean philosophy appear to annoy Plutarch considerably: first, their dismissal of the aporetic/dialectical spirit that Socrates embodies, and which Plutarch regards as central to philosophy, and second, that Stoics and Epicureans alike adopt a corporealist or materialist metaphysics, rejecting the intelligible realm (that comprises god, Forms, immaterial souls), which was essential to Platonism. The central line permeating Plutarch's relevant criticism is that Stoics and Epicureans contradict our common notions (see e.g. De communibus notitiis 1073C-1074F) and do not do justice to things themselves (De profectibus in virtute 75F-76A). Ironically, perhaps, Plutarch's polemical writings are chiefly of interest—but also of very great value—for the many quotations they contain from Stoics, Epicurus, and other authors whose works were not preserved into modern times, and for his references to and paraphrases of their views in other passages of works available to him but not to us. Were it not for Plutarch, our grasp of Stoic and Epicurean philosophy would be much less extensive than it is, and our ability to reconstruct and appreciate their ideas much reduced.