Most current definitions of blended learning refer to a blend of online and face-to-face instruction. It seems that few authors notice the irony that the definition of blended learning does not include the concept of learning at all. The problem with these definitions is that they are devoid of theory and thus lead to trial-and-error research. This paper argues that the definition of blended learning should be built around learning theory and should refer to a blend of direct instruction and learning-by-doing. The paper reports on research conducted to validate a model that puts behavioural and constructivist learning at right angles and considers if the two can occur simultaneously. The model is then placed in the context of a framework of knowledge management and from there a definition is derived that includes context, theory, methodology and technology.