The importance of software development expertise to our society and likewise the importance of education in this field are self-evident. At the same time it is undisputed that software development at the professional level is a complex activity. It must be presumed that the make-up of expertise required to successfully complete such activities will itself be non-simple, deserving of our attention. A hierarchical view of professional expertise is presented and a method for determining the fundamental principles making up lasting expertise is systematically derived. The method is applied to determine principles of software engineering expertise. The view presented provides a step towards a well founded understanding of the types of expertise needed for the activity of software development. Educators involved in courses releasing professionally recognised software developers should be interested to examine which aspects of the expertise-derivation they already utilise and which aspects could further benefit their courses.