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Exactly 300 years ago Gottfried Leibniz published his New System of the Nature of Substances, a rich and imaginative metaphysical account of pre-established harmony between created things. Leibniz went into print, he explicitly says, "mainly to benefit from the judgements of people who are enlightened in these matters, and who might be willing to give me advice - which I shall always be glad to receive, provided it shows a love of the truth, rather than a passion for preconceived opinions". Leibniz's letters are characterised by similar hopes for serious, positive and constructive discussion.

This century began with discussion of the kind Leibniz would have found worthwhile, as Louis Couturat and Bertrand Russell raised the relationship between Leibniz's logic and his metaphysics. It looks like it will end in the same constructive way, with some superb books from North America.

Catherine Wilson's illuminating Leibniz's Metaphysics was followed by R. C. Sleigh's Leibniz and Arnauld, a book hailed as a rival to Russell's in its seminal importance. And these are now joined by Robert Adams' Leibniz. Leibniz could not have hoped for a more thoughtful and penetrating, more careful, sensitive, and positive, examination of his ideas than this. It deals at length with three central topics: Leibniz's determinism, which connects with his concept-analysis doctrine of truth and his rejection of any identity between individuals in different possible worlds; his theism, which involves discussion of the ontological argument, divine perfection, existence, essence, and the relation of God to possibility; and his idealism.

As regards this last topic one wishes Adams had been able to interrogate Leibniz himself and not merely his writings. Out of the work by Adams and his American colleagues has crystallised another core question: how extensive and pervasive throughout Leibniz's mature period (1686 onwards) is the quite obvious and undeniable idealism of later years: that all that exists are mind-like monads and their perceptions? Adams here takes issue with those who have found a belief in the reality of matter in at any rate the beginning of this period. Given the already extremely high standards of the debate it is doubtful that this disagreement will be solved by a greater knowledge of and sensitivity to the texts and their historical surroundings. So, given the consensus about the interpretative issues, it would have been good if Leibniz himself could have been invited to explain. Given the evident "love of truth" exhibited in Adams's book, he surely would have welcomed it.

R. S. Woolhouse is professor of philosophy, University of York.