Frederic E. Clements was a leading ecologist during the formation of American ecology in the early 20th century. In constructing a theory of succession, he adopted a viewpoint of reductionism used in physiology. He recorded this idea in Research Methods in Ecology(1905) and Plant Succession(1916). In Research Methods, Clements understood the developmental process of community from the viewpoint of reductionism: Community developed gradually toward stabilization through its interaction with physical environment. And he thought that the stage of stabilization was the unchangeable state of community. Therefore, his succession theory had a teleological tendency. In Plant Succession, the idea of the stage of competition was newly added to the process of developmet. Clements said that competition implied decrease in the amount of water and light available for each individual, and that it affected the response of each plant through them. In addition, he frequently changed the term, 'stabilization', to 'climax', and divided the latter by climatic factors, into subclimax and potential climax. Thus, Clements understood the developmental process of community from the reductionist viewpoint, too. Also, the stage of climax was the state of incomplete equilibrium with physical environment, which another community could invade. Due to this instability of the stage of climax in his succession theory, the teleological tendency was weakened.