The concept life course implies a form, a pattern, a sequence of elements that together constitute a coherent observable configuration. The concept is abstract, however. The kinds of elements used to identify the shape of the life course must be specified by the analyst. Sociologists use different kinds of elements, but they are all defined in terms of social roles or positions in a social structure. The elements may be educational, work, or family roles or positions. It is possible to think of careers in all of those domains as well as others, but each of them is just a single strand in a more complex configuration called the life course. They are simultaneous and interlocking careers.