In 1973 a workshop was held at The University of Western Ontario on topics of common interest to philosophers and linguists. This volume con tains most of the papers presented at the workshop. Also included are previously unpublished essays by R. Dougherty and H. Lasnik as well as a comment on G. Lakoff's paper by B. van Fraassen. K. Donnellan's paper was presented at the workshop and subsequently appeared in The Philosophical Review. We thank the editors of this journal for permission to publish the paper here. The papers by D. Lewis, R. Stalnaker, G. Lakoff, B. Partee and H. Herzberger appeared earlier in Journal of Philosophical Logic by arrangement of the editors with B. van Fraassen and D. Reidel Publishing Company. The editors thank the officers of The University of Western Ontario for making the workshop possible and Pauline Campbell for making the workshop work. THE EDITORS DAVID LEWIS COUNTERFACTUALS AND COMPARATIVE POSSIBILITY* In the last dozen years or so, our understanding of modality has been much improved by means of possible-world semantics: the project of analyzing modal language by systematically specifying the conditions under which a modal sentence is true at a possible world. I hope to do the same for counterfactual conditionals. I write A 0-C for the counter factual conditional with antecedent A and consequent C. It may be read as 'H it were the case that A, then it would be the case that C' or some more idiomatic paraphrase thereof."

The purpose of this brief introduction is to describe the origin of the papers here presented and to acknowledge the help of some of the many individuals who were involved in the preparation of this volume. Of the eighteen papers, nine stem from the annual fall colloquium of the Depart ment of Philosophy at the University of Western Ontario held in London, Ontario from November 10 to November 12, 1967. The colloquium was entitled 'Philosophical Logic'. After some discussion, the editors decided to retain that title for this volume. Von Wright's paper 'On the Logic and Ontology of Norms' is printed here after some revision. A. R. Anderson commented on the paper at the colloquium, but his comments here are based upon the revised version of the von Wright paper. The chairman of the session at which von Wright's paper was read and discussed was T. A. Goudge. Aqvist's paper 'Scattered Topics in Interrogative Logic', and Belnap's comments, 'Aqvist's Cor rections-Accumulating Question-Sequences', are printed as delivered. The chairman of the Aqvist-Belnap session was R. E. Butts. Wilfrid Sellars' paper 'Some Problems about Belief' is printed as delivered at the col loquium, but 'Quantifiers, Beliefs, and Sellars' by Ernest Sosa is a revision of his comments at the colloquium. That session was chaired by G. D. W. Berry. Ackermann's paper 'Some Problems oflnductive Logic', as well as Skyrms' comments, are printed as delivered."

In 1973 a workshop was held at The University of Western Ontario on topics of common interest to philosophers and linguists. This volume con tains most of the papers presented at the workshop. Also included are previously unpublished essays by R. Dougherty and H. Lasnik as well as a comment on G. Lakoff's paper by B. van Fraassen. K. Donnellan's paper was presented at the workshop and subsequently appeared in The Philosophical Review. We thank the editors of this journal for permission to publish the paper here. The papers by D. Lewis, R. Stalnaker, G. Lakoff, B. Partee and H. Herzberger appeared earlier in Journal of Philosophical Logic by arrangement of the editors with B. van Fraassen and D. Reidel Publishing Company. The editors thank the officers of The University of Western Ontario for making the workshop possible and Pauline Campbell for making the workshop work. THE EDITORS DAVID LEWIS COUNTERFACTUALS AND COMPARATIVE POSSIBILITY* In the last dozen years or so, our understanding of modality has been much improved by means of possible-world semantics: the project of analyzing modal language by systematically specifying the conditions under which a modal sentence is true at a possible world. I hope to do the same for counterfactual conditionals. I write A 0-C for the counter factual conditional with antecedent A and consequent C. It may be read as 'H it were the case that A, then it would be the case that C' or some more idiomatic paraphrase thereof."