There are many spontaneous conceptions related to the principle of action and reaction for two bodies in static contact. A study of a broad sample of students showed Newton's third law to be a great unknown for most of them. The conceptions were found to be consistent, forming authentic minitheories (implicit theories) with general laws governing the interactions. This consistency evolves over the course of the students' education, reflecting changes in their modes of learning. (Contains 2 figures and 2 tables.)