Between Rene Magritte’s 1926 drawing ‘Ceci n’est pas une pipe’ and Michael Craig-Martin’s 1973 sculpture ‘An Oak Tree’ is made apparent the final evolution and subsequent conundrum of contemporary art. In Magritte’s drawing the viewer sees a carefully rendered visual representation of a pipe floating on the page above the drawn words of the title (which translates as ‘This is not a pipe’) in a style reminiscent of a botanical text book. In Craig-Martin’s sculpture the viewer sees a glass of water on a plain glass shelf placed above head height while below left on the wall a text by the artist pre-empts questions and their answers arising from the work.
The former informs the viewer that not only is the drawing of the pipe not a pipe but neither are the words “this is not a pipe” (to what does the word (or even the drawn representation of the word) “this” refer? Is it the drawing of the pipe? Is it the words? Or is it the word ‘this’ itself?), and in a very simple singular gesture Matisse undermines the language systems (visual and verbal) on which human beings rely to navigate their world.  We can only know a thing if it is named. But the name is not the thing.  This may appear obvious but surely it proves that we can truly know nothing. This statement has been a fundamental question of philosophy since Plato considered the flickering shadows on his cave wall.
With ‘An Oak Tree’ Craig-Martin completes the work begun by Duchamp in 1917 with ‘Fountain’ by claiming that not only can anything be art if the artist declares it to be, but that the artist can declare it to be anything he wishes it to be. The glass of water on a glass shelf is not a glass of water on a glass shelf. It is an oak tree, in as much as the words “an oak tree” cannot be an oak tree. Craig-Martin states, in a gesture as equally simple and devastating as Matisse’s, that art is a more powerful tool for navigating the world than is the word, and also that art, and subsequently life, can, and does, lie.
 For a full (if highly idiosyncratic) exploration of the philosophical implications of Matisse’s work see Michel Foucault, This Is Not A Pipe, translated by James Harkness, University of California 1983
 See Jacques Derrida’s meditation on Death as an unpassable and therefore unknowable barrier ‘Aporias’, translated by Thomas Dutoit, Stanford University Press 1993