This paper presents a conceptual analysis of the nature of teaching and similar practices (including law, psychiatry, and social work), and examines how these differ from other practices. Chapter I defines practice; discusses common elements of practices (such as skills, knowledge and outputs); and describes teaching as an indeterminate practice whose outputs cannot be distinctly specified, and whose materials are human beings. Chapter II investigates the nature of uncertainty and commitment in indeterminate practices; explores how skills and knowledge are adapted to deal with uncertainty; and examines procedures that lead to apparently competent performance, given uncertainty about skills and outputs in indeterminate practices. Chapter III analyzes the nature of competence in practice, and suggests that the usual concept of competence may need to be altered for indeterminate practices, where (1) competence often results from not knowing exactly what produces competent performance; and (2) commitment of the materials of practice (such as students) may be a more important component of competence than practitioners' skills and knowledge. Finally, chapter IV explores the social features of practice; identifies areas where competence may need to be adapted to the social character of practice; and considers the importance and implications of viewing competence in social, rather than technical, terms. (Author/MJL)