In ‘Joyce, Mallarmé and the Press’ and ‘Catholic Humanism and Modern Letters’ (both 1954) McLuhan blasted the pretense of the artist who would be “the signer of a forged check on our [own] hopes and sympathies”. Instead:

The artist has merely to reveal, not to forge the signatures of existence.  (…) All those pseudo-rationalisms, the forged links and fraudulent intelligibility which official literature has imposed on existence must be abandoned. (Joyce, Mallarmé and the Press) 

In this angelic view [“that school of thought for which the external world is an opaque prison”] the business of art has nothing to do with the analogy of cognition nor with our miraculous power to incarnate the external world. It is a means rather to lift us [angelically] out of our [imprisoned] human condition (…) Reality is not to be trusted or revered but to be remade by social engineers. (Catholic Humanism and Modern Letters)

He recognized that the class of such “social engineers” included many of those whom he himself regarded as the greatest artists of the century:

Talk about blind spots in regions of maximal impact! Looking at The Diabolical Principle [Wyndham Lewis, 1931] just now, I read loud and clear that art must be totally environmental. It must be the content of nothing whatever. (…) Lewis wants nothing less for Art than the power to create total environments for Life and Death. (…) I find it a bit staggering to confront Lewis as a man who really wanted to be Pontifex Maximus of a magical priesthood. I suppose Yeats, Joyce and Pound had similar aspirations. Their priesthood was to create new worlds of perception. They were to be world engineers who shaped the totality of human awareness. (…) The environment as ultimate artefact. (McLuhan to Wilfred Watson October 4, 1964, National Archive Canada)

With the characterization that such art “must be the content of nothing whatever”, the implied charge was that it aspired to be the ground of everything, including itself: “nothing less (…) than the power to create total environments for Life and Death”.  But not only was genuine art called on the contrary “merely to reveal, not to forge the signatures of existence”, but all art needed to be assessed as figure. As a type of finite human making, its ability to express was in the first place a reflection of the prior environmental ground enabling it to do so and even to be at all. This was the conviction at the heart of McLuhan’s realism.