Learning Objects have been defined as small as a drop and as broad as the ocean. The real question is if learning objects can be almost anything what is not a learning object? In this paper we will propose a distinction among media objects, knowledge objects, instructional strategy objects, and learning objects. We will define and illustrate knowledge objects, knowledge structures, and knowledge bases. The paper will propose that learning objects are a combination of instructional strategy objects with a knowledge base. The paper proposes that knowledge objects, knowledge structures, and knowledge bases provide a much more reusable form of knowledge representation than many of the current approaches to learning objects. And finally we will discuss these ideas about instructional components and objects in the context of mental models, the knowledge objects inside the head of our learners.