Since 1960' s with a background of expansion of graduate schools, the adult education study in the United States has remarkably progressed. It can be said that the research on adult education has been developed on a base of self—directed learning (SDL)
because many researchers considered it as a central concept in adult education. The proliferation of SDL research, however, along with vagueness of concept and diversity of approaches, prohibits us from understanding SDL theory in perspective.
The purpose of this paper is to clarify the advances and issues in SDL theory by reviewing SDL researches chronologically.
First I analyzed the dissertations on SDL quantitatively using the database of Dissertation Abstract International. As a consequence I found there are 388 dissertations presented from 1966 to September 4th, 1998. The average number of dissertations annually by 1970' s was 1.0 to 2.4, but it increased dramatically in 1980' s. Especially after mid-1980' s it went over twenty.
Then I analyzed SDL researches qualitatively. I selected a number of researchers to be considered from the viewpoint of impact and contribution toward the development of SDL theory, and classified them into three groups : the first generation, the second generation and the third one. As the first generation, who worked as a originator, I listed up C. O. Houle, A. Tough, and M. S. Knowles.
The second generation is a group which filled the role of making the research done by the first generation exqusite and of examining it critically. L. M. Guglielmino, S. D. Brookfield, G. E. Spear and D. W . Mocker represented this generation. And succeeding group which adjusted the discord between the first generation and second one is referred as the third generation. It includes H. B. Long, P. C. Candy, P. Jarvis, P. Cranton, R. G. Brockett & R. Hiemstra, and M. Tennant who have appeared in 1990's.
I focus on the first and the second generations here.