The contrast between the strategies of research employed in reductionism and holism masks a radical contradiction between two different scientific philosophies. We concentrate in particular on an analysis of the key philosophical issues which give structure to holistic thought. A first (non-exhaustive) analysis of the philosophical tradition will dwell upon: a) the theory of emergence: each level of organisation is characterised by properties whose laws cannot be deduced from the laws of the inferior levels of organisation (Engels, Morgan); b) clarification (...) of the relations between the “whole” and the “parts” (Woodger, Needham); c) the ontological or epistemological nature of the emergent properties; are they a phenomenological reality or solely an artefact of the state of our knowledge? (Pepper, Henle, Hempel and Oppenheim); d) the proposition of the holistic theoretical and methodological model ( Novikoff, Feibleman). I then go on to examine the differences that exist between the reductionist and the holistic approaches at various levels of analysis: that is to say, the differences which affect their ontologies, methodologies and epistemologies respectively. I attempt to understand the spirit of a holistic approach to ecology by analyzing the major work of E.P. Odum Fundamentals of ecology (1953, 1959, 1971). I set forward what might be meant by the “holistic approach”, which is implicated in all the different levels of organisation at which the problem of “complexity” is debated. Ecology presents itself as an “holistic science” and Odum’s book offers a vision of the world which dates far back in the history of philosophy. By looking at the three different editions of this fundamental text on ecology, we may become aware of the evolution of Odum’s thought. In fact, only in the third and last edition is there a conscious appropriation of the holistic approach (by using the theoretical models of Feibleman who, for his part, refers to Novikoff). However, even when formally referring to the theory of emergence (that is to say the ontological nucleus of every holistic approach), Odum’s systemic analysis presents the same logical errors, which push him back into the reductionist domain. Above all, in his examination of the main concepts of “population”, “community” and “ecosystem”, there is a misunderstanding of the profound difference between “collective properties” and “emergent properties”. Moreover, the cybernetic models of Odum’s systemic analysis (introduced into ecology by Margalef), allowed him to vastly oversimplify his methodological task: in fact, neither how many levels nor which levels of organization are fundamental for the study of each individual level is clearly marked. Finally, Odum analyses the ecosystem as composed of energetic flux and cycles of matter, referring to the trophic-dynamic vision of Lindeman. That is to say, in my opinion, he juxtaposes a reductionistic methodology and epistemology to an holistic ontology. (shrink)