Introduction
The Generic strategy framework (Porter, 1980) comprises two alternatives each with two alternative scopes. Unfortunately Porter confuses this by asserting that Focus - i.e. Narrow Scope - is the THIRD generic strategy.
Clearly, however, as it depends on the former two major dimensions it cannot stand alone as a strategy itself. It is better to use the model as a four-cell framework:
Definition
There are in essence only two generic strategies, Differentiation and Low-Cost Leadership each with a dimension of Focus - broad or narrow.