 The first assumption is that concepts are semantic entities rather than psychological entities. Concepts are constituents of contents. Attitudes towards contents are psychological occurrences, but the contents themselves are not psychological entities. They, and the concepts they contain, are abstract  entities.[4]  The second assumption is that, although concepts are abstract entities, mastering a concept is a psychological achievement. We need a cognitive account of what it is to master a concept, even though concepts are not psychological entities.