In the nineteenth century, artists were primarily concerned with ideas of truth and beauty. The aesthetic theorist John Ruskin, who championed what he saw as the naturalism of J. M. W. Turner, saw art's role as the communication by artifice of an essential truth that could only be found in nature.^[27]

The definition and evaluation of art has become especially problematic since the 20th century. Richard Wollheim distinguishes three approaches: the Realist, whereby aesthetic quality is an absolute value independent of any human view; the Objectivist, whereby it is also an absolute value, but is dependent on general human experience; and the Relativist position, whereby it is not an absolute value, but depends on, and varies with, the human experience of different humans.^[28]

The arrival of Modernism in the late nineteenth century lead to a radical break in the conception of the function of art,^[29] and then again in the late twentieth century with the advent of postmodernism. Clement Greenberg's 1960 article "Modernist Painting" defines modern art as "the use of characteristic methods of a discipline to criticize the discipline itself".^[30] Greenberg originally applied this idea to the Abstract Expressionist movement and used it as a way to understand and justify flat (non-illusionistic) abstract painting:

Realistic, naturalistic art had dissembled the medium, using art to conceal art; modernism used art to call attention to art. The limitations that constitute the medium of painting – the flat surface, the shape of the support, the properties of the pigment — were treated by the Old Masters as negative factors that could be acknowledged only implicitly or indirectly. Under Modernism these same limitations came to be regarded as positive factors, and were acknowledged openly.^[30]

After Greenberg, several important art theorists emerged, such as Michael Fried, T. J. Clark, Rosalind Krauss, Linda Nochlin and Griselda Pollock among others. Though only originally intended as a way of understanding a specific set of artists, Greenberg's definition of modern art is important to many of the ideas of art within the various art movements of the 20th century and early 21st century.

Pop artists like Andy Warhol became both noteworthy and influential through work including and possibly critiquing popular culture, as well as the art world. Artists of the 1980s, 1990s, and 2000s expanded this technique of self-criticism beyond high art to all cultural image-making, including fashion images, comics, billboards and pornography.