The abstract qualities in art are those which are independent of a work's resemblance to external reality. The arrangement of lines, forms, tone and colour, even in a painting depicting an aspect of the known world, can be viewed as a series of non-representational relationships. Such patterning has often been appreciated for its own sake; music without vocal narrative elements tends to be enjoyed in a similar manner.
From the late 19th century onwards visual abstract or formal qualities were increasingly emphasised, analysed and finally isolated by painters; see the entries for Post-Impressionism, the Fauves and Cubism.