Hughes, together with other systems-based artists, frequently produced works in which one form, or group of forms, was used as the basis for a set of related images. Systems artists saw a close link between the process and structure of abstractive construction and musical composition - for example, this Four Part Painting may be seen as the visual equivalent of a musical theme and variations. Each of the four units in this work is a variant of the same group of orthogonal and slanting bars. There are variations in the placement of these bars and how they overlap each other, and these differences are emphasised by the varying use of colour. The four part set is held together to form a coherent whole, partly by the similarity of the geometry, partly by combinations of the same colours being used throughout the set. And in this, as with all systematic constructive abstraction, a full appreciation of the work is achieved by a close study of its detail as well as by responding to its overall visual impact.