This paper identifies and characterizes the existence of a specific class of "constojcts" which may be particularly difficult to learn and understand. Their difficulty necessitates conceptual change, which is a form of learning which we define in the context of this class of constructs. Our explanation seems to fit a diverse set of data concerning the difficulty in learnirig science concepts of this nature. Instructional implications for how w e can overcome this barrier to conceptual change will also be entertained.
