The hypotheses must be conceptually clear. This point is implicit in the proceeding criterion. The concepts utilized in the hypothesis should be clearly defined not only formally but also, if possible, operationally.
Formal definition or explication of the concepts will clarify what a particular concept stands for, while the operation definition will leave no ambiguity about what would constitute the empirical evidence or indicator of the concept on the plane of reality.
An ambiguous hypothesis characterized by undefined or ill-defined concepts cannot be tested since, understandably, there is no standard basis for knowing what observable facts would constitute its test.
It is advisable that the concepts embodied in the hypotheses be defined in a manner commonly accepted and communicable. This would ensure continuity in researches and go a long way in bringing about a cumulative growth of scientific knowledge.