This lecture was designed as an introduction to Plato's theory of Forms. Reference is made to key passages of Plato's dialogues, but no guidance on further reading is offered, and numerous controversies about the theory's interpretation are left in the background. An initial sketch of the theory's origins in the inquiries of Plato's teacher Socrates is followed by an explanation of the Forms’ primary characteristic, Plato's metaphysical separation of them from the sensible world. Other aspects discussed include the Forms’ metaphysical relation to sensible particulars, their ‘self-predication’, and the range of items that have Forms. Finally, the envisaged structure of the world of Forms is illustrated by a look at Plato's famous Cave simile.

During the last four decades historians of ancient logic have become increasingly aware of the importance of Diodorus Cronus and his pupil Philo as pioneers of the propositional logic which came to flourish in the Stoa. Their direct influence has so far been recognised in two main areas of Hellenistic controversy – the validity-criteria for conditional propositions, and the definition of the modal terms ‘possible’ and ‘necessary’. But some broader questions have not been satisfactorily answered. What were Diodorus' own philosophical allegiances and antecedents? What is his place in the history of Greek philosophy? How far-reaching was his influence on the post-Aristotelian philosophers?

There was little chance of tackling these questions confidently until 1972, when Klaus Döring published for the first time the collected fragments of Diodorus, in his important volume Die Megariker. Meagre though they are, these fragments confirm my suspicion that Diodorus' philosophical background has not been fully explored, and also that his influence on the three emerging Hellenistic schools – the Stoics, Epicureans, and Sceptics – was far wider than has hitherto been recognised. There has been much discussion as to which earlier philosophers played the most decisive part in shaping Hellenistic philosophy, and the respective claims of the Platonists and of Aristotle have never lacked expert advocacy. In all this, the claims of so obscure a figure as Diodorus have been underrated.

One of the reasons why the past three decades have been an exciting time for historians of Epicureanism has been the revival of work on the Herculaneum papyri – very much a team effort. But another equally good reason has been provided by a remarkable solo act, Martin Ferguson Smith's pioneering work on the second-century AD Epicurean inscription of Diogenes of Oenoanda – the largest of all Greek inscriptions to survive from the ancient world, a key text in the history of Epicurean philosophy, and an extraordinary snapshot of the (literally) monumental scale on which philosophical evangelism could be practised in the Roman empire.

Smith has, almost single-handed, discovered and edited well over 100 new fragments of the inscription. This enabled him in 1993 to publish his comprehensive edition of the augmented inscription. But that was not the end of his labours. Returning to the site of Oenoanda, he has unearthed a substantial body of new ‘new fragments’, and has hopes of uncovering more in future seasons. A recent batch was published in a 1998 article. In this paper I want to consider just one of them, New Fragment 128, which fills a hole in the existing fr. 33 of Smith's edition. Thanks to this discovery, Smith has been able to supply the line-ends of the missing col. IV, and likewise to join the previously lost line-beginnings of col. V to the already surviving line-ends of that column. In addition, he has been able to make very convincing improvements to his previous readings of column III.