What is measured by a psychological measure

In the case of every psychological measure one may ask the following three questions: (1) To what extent is it stable over repetitions? (2) To what extent does it measure what it purports to measure? (3) What is measured by the measure? The first two questions are concerned with reliability and validity and avoid the topic of content. The answer to the third question can only be given in terms of the shared conceptual system embedded in a natural language. The answer is identical to a description in such terms of how the person understands the item involved.