The fourth international rotifer symposium was Wednesday afternoon a tour of Edinburgh, includ held in Edinburgh, Scotland, August 18 - 25, 1985, ing a visit to the Palace of Holyrood, was arranged. hosted by the Institute of Terrestrial Ecology. This This was followed by an evening banquet with meeting continued the tradition of holding rotifer traditional Scottish entertainment. On Thursday symposia at three-year intervals. The first an evening most participants attended a fireworks dis nouncement of the fourth meeting was circulated at play which was part of the Edinburgh Festival. Fi the end of 1983 to almost 300 people whose names nally, an excursion to Loch Lomond and the Tros appeared on the mailing list of the international sach hills was arranged for the Saturday after the newsletter, Rotifer News. In total, 68 people from meeting. 23 countries attended the meeting. It is interesting The organisers would like to thank Mr. C. J. to note that, of these 68 participants, 21 had at Place and colleagues at the Institute of Terrestrial tended the first meeting, held in Linz, Austria, Ecology for their invaluable help in organising the 1976, and 13 had attended all three previous meet meeting and preparing the symposium volume for ings. publication. We are also grateful for financial sup As in previous symposia, some research topics port from the Royal Society, the British Council were identified in advance of the meeting as being and British Petroleum (Scotland).

Understanding the role of deduction in human reasoning has been an important activity in philosophy, logic, and more recetnly artificial intelligence. The basic patter of this kind of reasoning can be represented by conditional expressions of the form `if...then.' There are various kinds of conditionals that fit into this pattern, such as counterfactual conditionals (`if it were the case that A then it would be the case that B'), causal conditionals (`if A then causally B'), action conditionals (`if A then B is obtained'), conditional obligations (`if A then B should be brought about'), generic conditionals (`if A then normally B')etc. The common pattern to all these constructions is their conditional form which connects the antecedetn to the consequent in such a way that the antecedent represents a condition (or a context) for the consequent. The general question arises: is it possible to give a formal logical account of these constructions? This question is considered in this volume by a group of internationally recognized pure and applied logicians and computer scientists. Their papers reflect all the current research in this subject, and should serve as a guide for future development.