you want to find out anything from the theoretical about the methods they use, I advise you to stick closely to one principle: don't listen to their words, fix your attention on their deeds. To him who is a discoverer in this field the products of his imagination appear so necessary and natural that he would like to have them regarded by others, not as creations of thought but as given realities. These words sound like an invitation to you to walk out of this lecture. You will say to yourselves, the fellow's a working physicist himself and ought therefore to leave all questions of the structure of theoretical to the epistemologists. (Einstein, 1934) Science is the attempt to make the chaotic diversity of our sense-experience correspond to a uniform system of In this system single experiences must be correlated with the theoretic structure in such a way that the resulting coordination is unique and convincing. sense-experiences are the given subjectmatter. But the theory that shall interpret them is man-made. It is the result of an extremely laborious process of adaptation: hypothetical, never completely final, always subject to question and doubt. scientific way of forming concepts differs from that which we use in our daily life, not basically, but merely in the more precise definition of concepts and conclusions; more painstaking and systematic choice of experimental material; and greater logical economy. By this last we mean the effort to reduce all concepts and correlations to as few as possible independent basic concepts and axioms. (Einstein, I940) If we substitute the words and for the words physicists and science in the above quotations from Einstein, we will have succinctly stated the problem we ecologists face in ridding ourselves of our confusions of ideas with realities and in translating our observations and experiments into communicable knowledge as a logically uniform system of thought. The development of Ecology has been characterized by many controversies that appear to us to be largely in the realm of words rather than deeds. This is not surprising, however, because the highly complex nature of the relations between the environment and organisms often leads to both frustration in interpretation and to vagueness in generalization. The aggregate nature of vegetation and the ensuing abstract conceptual complexities as they are necessarily handled in language, have contributed to a compounding of this confusion. Such perennially current questions as Do communities really exist ?, Should the fundamental unit of study be the individual, the population, the community, or the ecosystem ?, Is the classification of communities desirable?, and Is the ecosystem so complex as to defy significant analysis ? appear by their context to be resolvable largely upon the basis of additional empirical phenomena. But, in reality, they can be enormously clarified through a proper knowledge of our medium of understanding and communication without recourse to new facts. We have become convinced that where controversy reigns for long periods in science, in spite of the discoveries and new techniques developed by generations of scientists, the difficulty is probably not so much inherent in the material as in the language in which it is being discussed. Language analysis provides an approach to the resolution of some of these difficulties. Several scientific fields have been illuminated by the use of these methods, the most prominent among them being physics and psychology. It seems to us that there might be some values here for the ecologist. We have investigated, in particular, the Theory of Signs (Morris, 1938) and applied these methods to the language in which our various concepts of the environment have been expressed. As a result we have been led to a reappraisal of this key concept in the structure of ecological knowledge. Although we cannot here deal with the Theory of Signs in great detail, we would like to present a brief resume before embarking upon our analysis of the concept environment.' We solicit patience with what may seem to be a tedious presentation of subtle details which we hope will give a background in the terminology and the concepts that we employ in our explanations. We hope that the reader will not leave us as Einstein thought his listeners might, convinced that this is not Ecology. We wish to express our appreciation to David Rynin for many helpful suggestions in the formulation of our concepts, but we do not imply that he is in any way responsible for what may prove to be our misuse of them. Albert Ulrich read the 1 Following semantic convention, the same word may appear in quotation marks, in italics, and in ordinary type. This indicates as the subject respectively the word, the concept, or the phenomenon of nature.