Every time I give a course as a biology teacher I come to a point where the class has to confront what science is. What is the difference between a scientific explanation and a nonscientific one? Why do scientists accept the theory of evolution, for example, and flatly reject creationism? The class is never wholly satisfied with the answers we find to these questions and although part of the difficulty may lie in my ability to teach or students' willingness to learn, most of the difficulty is the nature of the question.

It is not possible to give a short clear answer to the question: what is science? Much less to understand why some explanations pass as scientific and others don't. The reason, as Ziman's book points out, is that science is not an abstract category. It cannot be clearly delimited from non-science by a few criteria. Science is a natural kind and can be apprehended only through understanding the practices and behaviour of the scientific community.

I have an abiding interest in philosophy of science but bring to this review no professional authority beyond that implied by my being a scientist. The overriding comment I can make about this book is that it describes the science I know. Ziman's approach shows how practices in science give it its explanatory power and resilience in spite of the fact that many desiderata considered definitive to science such as originality, objectivity and disinterestedness are transgressed every day by some scientists.

The book is arranged as 10 chapters. The first four chapters introduce the problem and set the groundwork towards Ziman's answer which lies in an elaboration of the activities and customs of science. How do scientists communicate? How do they vet their own disciplines? How do scientists decide among competing theories? Ziman asks us to see science as a human activity and a social and cultural process. We should not, therefore, expect science to be defineable as an abstract category. Like any biological process, science is apprehended through its practices even if these change as science evolves.

Ziman adopts an encompassing view of science: learned research on Aristotle's "Rhetoric" and on nuclear physics are both included. Although they are easy to distinguish on several planes, there is no useful way to define one as science, the other not. What he would like to know is what they have in common as science.

Science has no discrete historical beginnings. It is an activity pursued by humans and therefore has arisen with them, but it seems to come out of prehistory. Consider the way science manifests itself in everyday life, from the brew master carefully watching over sugar conversion to the farmer applying fertilizer to the soil, to the policeman on the corner using radar to gauge the speed of an oncoming car. All are examples of science in application (technology) and their very existence implicates the existence of science in action (research). In just such a way we may surmise that agricultural practices in Mesopotamia implicate science in action prior to the development of written language.

Science is often presented as a system of progressive inquiry — but what exactly characterizes that system? Many suggest it is the method of science, but Ziman argues the methods of science are as varied as the disciplines. Although experiment is a hallmark of much good science, it is hardly useful to consider it a sine qua non of science. Where would we place Einstein's speculative inquiry on relativity prior to its experimental vindication? Science produces knowledge but this is not a process of simple discovery — it is action according to a particular plan. No matter how exploratory the research, it is always conducted with a plan in mind. Scientists often tout the important role of serendipity in the development of knowledge but serendipity is chance favouring the prepared.

Admitting that science has changed over the years, Ziman argues that science is usefully apprehended through an exemplary form, academic science, science done in the universities. Using academic science as a model he analyzes it in terms of norms central to it such as communalism, universalism, disinterestedness, originality and scepticism. Each of these norms is treated in its own chapter. Successive chapters embrace the subject from an increasingly inclusive perspective.

By communalism, Ziman refers to the fact that science is not a solitary activity. Scientists do not labour away in their solitude but require regular feedback (positive and negative) from their peers. Results are not really results until they are shared with a larger scientific community. This requires that they be published in the scientific literature and entry into these archives is controlled by the process of peer review. Scientists learn that to make this process most rewarding they have to present their findings in such a way that their reviewers are assured that their results are reproducible, logically consistent and that they are independent of the observer. Scientists often spend much more time planning than actually doing experiments. They ensure wherever possible that their findings are replicated and that appropriate controls are carried out.

By universalism, Ziman means that science cannot admit purely idiosyncratic views, or views generated from a particular (e.g., religious, corporate) perspective. Science is looking for a broader consensus. Science is interested more in general theories than in particular facts, and even the facts of science are only meaningful in terms of theory. The languages of scientific disciplines abound with constructs that formalize and systematize the phenomena studied. Formalism as exemplified by the systematization of knowledge and the development of a more precise vocabulary appeals to the ethos of universalism and communalism. It allows scientists to converge in discussion and facilitates communication within disciplines even though it may create walls between disciplines. The language used is stripped as much as it can be of its metaphors (except in form of models) and is largely descriptive. Mathematics provides a convenient communication tool giving explicit representation to categories and describing how they should behave.

Disinterestedness appeals to objectivity. Scientists strive to evaluate theories and findings without reference to their own personal interest. This norm is tested by much research undertaken by industry where the results of findings can have financial repercussions for the company that sponsors the research. However, the larger research community achieves something very close to the norm by the review process. Scientists who are not under the same constraints as those producing the research will review the manuscripts submitted to the literature. Ziman refers to the result of this process as consensual objectivity.

Science deeply values originality. To contribute to the literature one must convince reviewers that the findings are in some way new to science. This norm is important in evaluation of research proposals where the appeal to originality may involve extensive piecemeal addition to a well-accepted body of knowledge, as well as new ideas that may be highly critical of accepted views. Originality also forces scientists to be aware of what is happening in their research area. To achieve this mastery of the literature, scientists must focus on a limited set of problems; thus, Ziman sees the highly substructured nature of scientific disciplines as a response to the norm of originality.

Skepticism is the final norm discussed by Ziman and with it he reiterates many of the themes he develped previously. He first notes that organized skepticism acts as a curb to originality. Not everything new is worthy of inclusion in the literature. The peer review process approaches all findings with some level of skepticism and this norm pervades all argumentation in science, from simple dialogue to formal debates in scientific congresses.

In a world dominated by organized skepticism how can the community decide on one theory over another? Ziman appeals to an evolutionary model to explain this. Theories and hypotheses in every field are presented in the literature to be adopted or ignored by other research groups. Theories deemed to be useful (in generating potential experiments or new areas of study, for example) are reused and represented in subsequent publications. There may be periods where competing theories are adopted by different research groups. Even when debate apparently storms between such competing groups, the most important effect of such debate is to clarify criteria whereby one theory could be distinguished from another.

Through Ziman's approach we come to see the great resilience of science. Individual scientists may be blinded by the value of a pet theory but no matter how important the scientist, their commitment to the theory is not enough to make it accepted. Scientists with idiosyncratic views are powerless to convince the world by the force of their personality. Not only must their arguments be logically convincing, they must explain the types of phenomena that the discipline identifies as worth explaining and, in the long run, their theories must be found useful by other scientists. Thus, scientific credibility is measured in the marketplace of ideas. Science is not dictated from on high but emerges from its broad acceptance by individual practicing scientists.

In the final chapter Ziman asks, What is the basis of scientific belief? If objectivity is a myth, and induction leads to a general statement only through a metaphysical leap, what is the nature of scientific truth? Ziman reminds us that the problems of induction and objectivity pervade all human understanding. Scientists act as if they agree upon a shared external reality and this allows them to converge with one another in discussion and study of the world. The very same thing occurs in our everyday life. No matter how many times we experience the succession of day and night we are never absolutely certain about its occurrence in the future.

However, day and night are part of the general and scientific theory of planetary motion, which also explains seasons, tides, meteor showers and many other events. Acceptance of this theory guides a hugely diverse array of human activities both scientific and commonplace. This consilience of scientific theories — their ability to explain previously unrelated bits of the world — makes them particularly believable.

This book should be read by anyone interested in the philosophy of science. Although it rarely goes deeply into philosophical issues, it provides a realistic context within which to situate philosophical discussion. In doing so it succeeds in presenting a realistic view of science, warts and all. It is on such a plane that the value of science should be debated. I recommend this book highly. It is not an easy read but it is a rewarding one.

Martin Adamson is professor and Director of the Biology Program at the University of British Columbia.