area of science to the concepts and laws comprising a theory in another scientific area. Thus, reducibility of one science to another might hold ontologically, but not conceptually. But, in any case, as Ernest Nagel has pointed out, before we can meaningfully debate the reducibility of theories one to another, the respective theories must be highly developed and unambiguously articulated. 52 Since this condition is not presently satisfied by parapsychology, it is perhaps premature even to raise the reducibility issue with respect to this discipline.
Other topics of importance in the philosophy of parapsychology include issues involving our concepts of space, time, and causality that arise particularly in connection with the parapsychological evidence for precognition, 53 and the challenges to our usual concepts of force and conservation of energy which may be posed by the claimed results of psychokinesis experiments. More intellectual effort should also be spent on the examination of parapsychology as a case study in the sociology of science. Such studies might repay dividends in terms of our understanding of the role of scientific institutions, channels of publication, and peer pressures in the development (or inhibition) of particular areas of scientific research.
It should now be clear that there is much work to be done in the philosophy of parapsychology, and that the issues involved are sufficiently important and central to the concerns of philosophers to repay the time and effort invested in the study of them. Particularly where a subject matter as controversial and, at the same time, as challenging as parapsychology is concerned, we should heed the advice of Glanvill and not rule out its claims as impossible without engaging in a careful and open-minded philosophical analysis of them. But, equally, we philosophers should not accept the conclusions of parapsychology without critically investigating them, since, as William James advises us in the essay which concludes this volume: "Tactically, it is far better to believe much too little than a little too much; . . . Better a little belief tied fast, better a small investment salted down, than a mass of comparative insecurity." 54*