Abstract :
There is no (formal) theory of HCl-there is rather only an HCl theory vacuum. However, the requirements for a sensible understanding of the question are becoming clearer. There is no sensible understanding of theory in HCl outside an understanding of: HCl as a design discipline, the ontology of HCl, as including humans and computers, tasks and effectiveness, the conception of HCl as an expression of the general design problem which HCl theory is intended to solve, and HCl theory (and practice) differentiation. Within this understanding of HCl, which encompasses discipline, ontology, conception and epistemology, two types of progress concerning theory in HCl are described. The first concerns formal HCl theory and is currently associated with formalising, formulating and operationalising the general HCl design problem. The second concerns informal HCl theory and is currently associated with models and guidelines, and methods and tools
