This article explores the relationship between interpretation and what is normally called 'understanding'. It is argued that different modes of interpretation define different kinds of 'mental uptake' ('apprehension'), and that some modes of interpretation define types of apprehension for which the concept of 'understanding' is inadequate. It is also argued that given a mode of interpretation, the constraints of that mode are necessary in the sense that it is the constraints on how to interpret that define a mode of interpretation. Thus within a mode of interpretation (historical, literary) one cannot interpret freely. Indeed, unconstrained interpretation is not interpretation. In order to illustrate these points the article offers a detailed discussion of two examples. The interpretative debate over the Magna Carta is used to illustrate the difference between a constitutional and a historical interpretation. These two modes of interpretation are then contrasted with literary interpretation, the aim of which is appreciation.