The present article originated out of an attempt to re-edit the letters of Gilbert Foliot, whose career as abbot of Gloucester, bishop of Hereford, and bishop of London covered nearly half of the twelfth century (1139-87). The edition by J. A. Giles is thoroughly unsatisfactory: the text is un-trustworthy, there is no index, and no attempt has been made to date the letters or to arrange them in any coherent order. Nothing could be done at present about the text, since the necessary manuscripts could not be consulted; but it was possible to make an index and with its assistance to arrange the letters in some sort of order and assign to them approximate dates. The chief clues for dating are naturally the names of persons, usually ecclesiastics, mentioned in the letters, but it soon became evident that the only lists available of these ecclesiastics (other than bishops) are for the most part entirely unreliable, and that a complete revision of these lists is a necessary preliminary to any attempt at precise dating, not only of these letters, but also of twelfth-century documents in general. In the thirteenth century, when Patent and Close Rolls begin, there is more positive information, and still more when episcopal registers become available. Before that time, documents were rarely dated, and appointments and deaths of minor officials were not important enough to receive much notice from chroniclers. It is for this early period, when references have to be collected from a number of scattered sources and exact dates are rare, that revision is most needed, and to it we are confining our investigation.

The seventeenth century was one of the twelve during which, in spite of what geographers might regard as probable and proper, the two sides of the Mediterranean were in the hands of two separate and inimical civilizations, different in religion, morals, law, economy and knowledge. That sea was nevertheless a busy highway. The Levant trade, the most important of all for the French and the Italians, was also important for the English and the Dutch; but North Africa, from the Atlantic coast of Morocco to the Libyan desert, Barbary par excellence, was outside the European system of international law and conduct. Even when they were nominally at peace the Christians and the Moslems never trusted one another or succeeded for long in abiding by the rules on which they agreed. Both sides tried to enforce such rules by collective and vicarious punishments, by reprisals and by other devices to which men resort when there is no law between them. Each side, often in spite of express treaty stipulations, made slaves of prisoners from the other: the Islamic society was based on slavery, and the Latin states also manned their war-galleys partly with their own criminals but largely with Moslems captured at sea. To the seafaring men of Europe captivity in Barbary was a danger worse than shipwreck.

I have been asked to speak to-day on the ‘new philosophy’ which arose and gradually triumphed in the period between the birth of Bruno in 1548 and the death of Descartes in 1650. I propose to put a fairly wide interpretation on the word ‘philosophy’, as did all the great thinkers of our period. And I propose to begin by giving a fairly full, though necessarily very imperfect, synopsis of the old philosophy against which the new doctrines reacted and which they superseded. What I shall describe with the name of the ‘old philosophy’ is the theory of the universe which St Thomas had elaborated on the basis of such knowledge of the works of Aristotle as was available to him.