إما داخل في مفهوم الطرفين
Or the common feature is internal to the concepts of both terms.
In this case, the linking meaning is not an accidental feature observed externally; it contributes to how the two activities or descriptions are conceived. Running and flying both involve covering a distance, and the discussion treats speed as relevant to their comparison.
By contrast, lions are commonly characterized as brave, but courage is not an essential constituent of the animal-kind, nor does the biological idea of lion enter the definition of a brave person. This distinction between an intrinsic conceptual element and an accompanying quality is crucial.