The meaning of the New Criticism today is not just literacy but a shift to reading in depth (…) rather than the single-plane approach of the older literacy. (Electronic Revolution: Revolutionary Effects of New Media, 1959)

A passage from McLuhan’s 1953 ‘Trivial and Quadrivial’ essay tells us everything we need to know about his project: 

Joyce underlines the skill of Bloom’s social decorum in a peculiarly witty way. Homer’s Odysseus learns from Circe that after passing the Sirens there were two courses open to him. One is by way of the Wandering Rocks, which Jason alone had passed in the Argo. The other is the way of Scylla and Charybdis, rock and whirlpool. Odysseus avoids the labyrinth of the Wandering Rocks. But Bloom navigates both labyrinths safely, thus excelling Odysseus. The Rocks are citizens and society seen in abstraction as mindless, Martian mechanisms. The “stone” men are children of the sun, denizens of space, exempt from time (…) Opposed to them are “The Dead” (see last story in Dubliners) children of the moon, the Celtic twilight (“cultic twalette”), moving in the aquacities of time, memory, and sentiment. On these dual labyrinths of stone and water Joyce has built almost every line he has written. (emphasis added) 

There are “two courses” or “dual labyrinths” to all human action and experience. Known or unknown, all human beings constantly “navigate” each of the two and between the two in every present moment of their lives. These two courses are arrayed vertically in synchronic time such that each of us perpetually traverses also a third labyrinth between them. This is the famous ‘gap where the action is’.  As Eliot has it in one of his two epigrams from Heraclitus for his Four Quartets: ‘odos ano kato. The way between (‘odos as in ‘meth-od’) and above (ano as in ‘an-ode’) and below (kato as in ‘cath-ode’): one, two, three.

Those who do not know of this constant back and forth of katabasis and anabasis are

citizens and society seen in abstraction as mindless, Martian mechanisms. The “stone” men are children of the sun, denizens of space, exempt from time.

But these are “mindless Martian mechanisms” only “in abstraction”, as McLuhan notes, because navigating these courses cannot not be done by humans. And so also these “citizens”, who conceive themselves as living only in the sun, have in fact made the “twilight” journey from their everyday lives above, to and within the dark below: “the aquacities of time, memory, and sentiment”. Indeed, their deportment above as “mechanisms” always reflects this action below — but only behind their own backs. Each one of them has reconnoitered these nether regions over and over again — but in blackout mode and utterly unconsciously.

It seems necessary to postulate a profound motivation for such universal somnambulism. (Take Today, 192, emphasis added)

This watery environment is therefore the last thing that human fish of this ilk can come to know.  But they can come to know it¹ and exactly as the spectrum of sensory thresholds through which all their experience, individually and collectively, is ordered.²

Now McLuhan had this tiered model of human being in mind, at lest vaguely, from the very start of his career. A letter to his family from Cambridge on Dec 6, 1934 records:

Of late I have been wayfaring among the work of T.S. Eliot (…) the poems I am reading [Poems 1909-1925] have the unmistakable character of greatness. They transform, and diffuse and recoalesce the commonest every day occurrences of 20th cent. city life till one begins to see double indeed — the extremely unthinkable character, the glory and the horror of the reality in life, yet, to all save the seer, [obscured and unknown] behind life… (Letters 41, emphasis added)

Eliot’s Norton lectures at Harvard (The Use of Poetry and The Use of Criticism, 1933) had just been published at this time, doubtless to enormous interest in Cambridge (where repeated attempts had been made to add Eliot to the English School faculty, especially by Eliot’s friend, I.A. Richards). McLuhan’s letter to his family had perhaps already been influenced by a passage from the lectures that he would never stop citing for the rest of his career:

What I call this “auditory imagination” is the feeling for syllable and rhythm, penetrating far below the conscious levels of thought and feeling, invigorating every word; sinking to the most primitive and forgotten, returning to the origin and bringing something back, seeking the beginning and the end. It works through meanings, certainly, or not without meanings in the ordinary sense, and fuses the old and obliterated and the trite, the current, and the new and surprising, the most ancient and the most civilized mentality.³

For McLuhan, this dynamic ano-kato movement (“returning to the origin and bringing something back“) was “the centre of the poetic process [and of the cognitive process in general that all great art mirrors in some way⁴], which Mr. Eliot, among others, has revealed in our time.”⁵

McLuhan’s 1943 Ph.D. thesis on Nashe told the story of these tiers or levels of life in terms of a background “quarrel” of the three disciplines of the trivium between 400 BC and 1600 AD. His 1946 paper on ‘An Ancient Quarrel in Modern America’ brought the story into the present day.  And for the following 35 years of his lifetime he would continue in a whole series of ways to investigate this notion of the synchronic dynamic of experience and to attempt to communicate his findings to the world.

The most direct of these ways (although nothing in this area is properly said to be direct) was to describe, over and over and over again, this “multi-level” perception of human being (dual gen!):

1947
the awareness of the unity of mythopoeic activity in history and art (…) has given modern man a sense once more of the simultaneity of all history seen at the psychological and intellectual level, as well as of the close bonds between all members of the human family past and present. (Inside Blake and Hollywood )

1947
Even [Etienne] Gilson (…) has no developed sensibility in contemporary art. I heard him on the puns in St Aug’s Confessions. He noted that they were inseparable from the multi-levels of simultaneous presentation without seeing that this is precisely our contemporary “cubist” sensibility. (McLuhan to Walter Ong, December 1947)⁶

1951
This secret [of Dante] consists in nothing less than a fusion of the learning and the creative processes in the analysis and reconstruction of the aesthetic moment of arrested awareness. This peculiar fusion of the cognitive and the creative by an act of retracing the stages of apprehension was arrived at by Joyce as a result of the prior discovery for the technique of fission [aka the discernment of plural levels] of the moment of aesthetic awareness. (…) In art as in physics fission preceded fusion. (The Aesthetic Moment in Landscape Poetry)

1951
this kind of single-level awareness [of Dos Passos] is not possible to anybody seriously manipulating the multiple keyboards of Joyce’s art. (Dos Passos: Technique vs. Sensibility)

1952
The multi-leveled consciousness fostered by modern physics and anthropology is matched in the contemporary arts of music, poetry, and painting.  The unilateral perspectives of nineteenth century biological theory cannot be imposed even in an academic milieu any longer. (Review of Auden: An Introductory Essay)

1953
The theme of this admirable work is that Herbert’s work is embedded in the matrix of orthodox Christian experience.  St. Thomas pointed out that all levels of meaning are contained in the literal. Miss Tuve says of Herbert that “he reads the spirit in the letter. Not into but in: he writes in symbols because he thus sees it as a web of significance not as a collection of phenomena (…) He writes not of events and facts, but of meanings. and values, and he uncovers rather than creates these meanings.” This sort of approach, now widely accepted, really speIls the end of the Cartesian era of culture. (Symbolist Communication, review of A Reading Of George Herbert, by Rosemond Tuve)

1953
[Bloom’s bar of] soap is a sign of grace uniting earthly and stellar, hermetic and astrologic, East and West labyrinths. These two levels of reality, which are in conflict all during Bloomsday, are thus reconciled among the stars. In the same context Dante is invoked obliquely as another sign of the reconciliation of Bloom and Stephen. For Dante, like Joyce and Eliot, employs grace to reconcile East and West. Reconciliation is not merging, however. (James Joyce: Trivial and Quadrivial)

1953
the trivium and quadrivium represent seven crossroads for the meeting of the various degrees and levels of reality.  (James Joyce: Trivial and Quadrivial)

1953
The trick is in finding the principle of intelligibility (…) in active relationships in existing dynamic situations. (The Later Innis)

1954
a passage of Greene, Lyly, or Nashe is not prose in the 18th or 19th century sense. The focus of attention has to be readjusted for changes of tone and attitude in every sentence. Print had not yet imposed its massive mechanical weight to level off the oral and colloquial features of prose. (New Media as Political Forms)

1955
Sixteenth-century prose still retains many of the rapidly shifting perspectives of multiple levels of tone and meaning which characterize group speech. It took two centuries of print to create prose on the page which maintained the tone and perspective of a single speaker. The individual scholar, alone with his text, had to develop habits of self-reliance which we still associate with the virtues of book culture. (Historical Approach to the Media)

1957
the poem [The Ancient Mariner] achieves a kind of continuous parallel between two levels of action, as does Joyce’s Ulysses in moving simultaneously in modern Dublin and ancient Ithaca. And it is in this same way that Tiresias in The Waste Land moves “between two lives.”

1957
Oral disputation and multi-level comment on texts were the natural result of oral teaching. Multi-level awareness of linguistic phenomena and of audience structure held up during print’s first century, but swiftly declined thereafter, since the speedy linear flow of printed language encouraged single perspective in word use and word study. (The Effect of the Printed Book on Language)

1957
For 500 years our idea of efficacy and efficiency was rooted in the technology of explicitness. To make happen and to explain scientifically have both meant the consecutive spelling out of consequences, one at a time. In the electronic age we enter the phase of the technology of implicitness in which by grasp of total field relationships we package information and deliver messages on many levels, all in an instant. (The Subliminal Projection Project)

1958
Electronic media are not mechanical but post-mechanical, and they evoke very different attitudes of mind from the mechanical age. On all sides we can see the rise of the “oral man” once more, the man whose awareness is shaped by the simultaneous flow of information from every quarter at once, a man who takes for granted that any situation has many levels at once. (Media Alchemy in Art and Society) 

1959
The multilayered montage or “transparency,” with its abridgement of logical relationships, is as familiar in the cave painting as in cubism. Oral cultures are simultaneous in their modes of awareness. Today we come to the oral condition again via the electronic media, which abridge space and time and single-plane relationships, returning us to the confrontation of multiple relationships at the same moment. (Myth and Mass Media)

1959
A low definition form like ordinary speech operates on many levels at once, and manuscripts were close to speech in offering a multi-leveled discourse to the reader. But print being of high visual definition did not exact the degree of participation that the manuscript did and does. Print could be read fast on one level… (Supplement to ‘Electronics and the Changing Role of Print’)

1960
The modern world of dynamics is an all-at-once world in which there cannot be single levels or one-thing­-at-a-time awareness. (The Medium is the Message)

1960
Automation depends upon an exactly syncronized information flow from electronic tapes, and substitutes the multi-levelled complex for the single-plane assembly line. (Report on Project in Understanding New Media)

1960
dialogue  (…) depends upon an everyway simultaneous flow which is a very far cry indeed from the one direction, one level flow of the printed page, or of the lecture platform. Electronic technology instructs the world again with simultaneous, every direction information flow. We cannot choose but live this way under electronic conditions. (Report on Project in Understanding New Media)

1960
With radio it is easy to notice one of the major features of electronic media, namely the powerful drive toward the extension of human dialogue into all levels of human affairs. (Report on Project in Understanding New Media)

1960
The barbarian plays it by ear. The civilized man plays it by eye. The barbarian lives in the all-at-once world of many directions and many levels of meaning at a single moment. Whereas the literate man lives by the eye, one-thing-at-a-time, one direction at a time, one level at a time. (Report on Project in Understanding New Media)

1960
mythic forms of explanation explicated all levels of any situation at the same time.  (‘Introduction’ to Explorations in Communication)

1960
Multi-levelled exegesis of⁷ Ovid or Virgil or the Scriptures was not only a medieval mode of reading and writing. It preceded Christianity and was the norm among ancient “grammarians.” To-day it is again the norm in physics, in psychology, in poetry and the arts. (Grammars for the Newer Media)

1962
there is nothing subliminal in non-literate cultures. The reason we find myths difficult to grasp is just this fact, that they do not exclude any facet of experience as literate cultures do. All the levels of meaning are simultaneous. (Gutenberg Galaxy, 72)

1962
Senecan antithesis and “amble” (…) provided the authentic means of scientific observation and experience of mental process. When only the eye is engaged, the multi-levelled gestures and resonances of Senecan oral action are quite impertinent. (Gutenberg Galaxy, 103)

1962
To the oral man the literal is inclusive, contains all possible meanings and levels. So it was for Aquinas. But the visual man of the sixteenth century is impelled to separate level from level, and function from function, in a process of specialist exclusion. The auditory field is simultaneous, the visual mode is successive. (Gutenberg Galaxy, 111)

1962
The study of the Bible in the Middle Ages achieved conflicting patterns of expression which the economic and social historian is also familiar with. The conflict was between those who said that the sacred text was a complex unified at the literal level, and those who felt that the levels of meaning should be taken one at a time in a specialist spirit. (Gutenberg Galaxy, 112)

1962
The scholastic method was a simultaneous mosaic, a dealing with many aspects and levels of meaning in crisp simultaneity. (Gutenberg Galaxy, 129)

1962
Structuralism as a term does not much convey its idea of inclusive synesthesia, an interplay of many levels and facets in a two-dimensional mosaic. But it is a mode of awareness in art language and literature which the West took great pains to eliminate by means of Gutenberg technology. It has returned in our time, for good or ill…  (Gutenberg Galaxy, 230-231)

1963
It is important to observe that the quality of the new “structural,” as opposed to the old lineal, sequential and mechanical, is the quality of the simultaneous. It is the simultaneous “field” of multitudinous events in equipoise or interplay that constitutes the awareness of causality that is present in ecological and nuclear models of perception today. Our electric mode of shaping the new patterns of culture and information movement is not mechanical but biological. (We Need a New Picture of Knowledge)

1963
In obtaining an eye for an ear, Western man clearly abandoned depth or structural knowledge in favor of applied knowledge. For the phonetic alphabet gave him the means of translating and reducing the complexities of the ear world to the flat retinal level of visually organized data. With Gutenberg came a further stage of this transfer of multi-leveled awareness into the typographic forms of exactly repeatable data. This very large step of transferring a manual craft into a mechanical form was done strictly within the compass of phonetic technology; that is, the further analysis of functions into uniform segments of movable and replaceable kind was the step that created at once the infinitesimal calculus, the uniform citizen armies of Napoleon, and the assembly lines of mechanical industry. (We Need a New Picture of Knowledge)

1963
The Gutenberg era of our Western world saw the suppression of dialogue in favor of visual systems and blueprints of knowledge laid out in “subjects” and “fields” packaged in varying degrees of processing and predigestion. Our Gutenberg technology enabled us to “apply” knowledge freely; that is, we learned how to translate every sort of knowledge into single planes of homogeneous kind. Applied knowledge is a process of translation and reduction of varied forms into a single form. This process of homogenization, as it gathered momentum, struck panic into the nineteenth century mind, but it greatly increased property and wealth and made the first consumer society. (We Need a New Picture of Knowledge)

1964
Concern with effect rather than meaning is a basic change of our electric time, for effect involves the total situation, and not a single level of information movement. (Understanding Media, 26)

1964
The first great change in [prose] style came early in the eighteenth century, when the famous Tatler and Spectator of Addison and Steele discovered a new prose technique to match the form of the printed word. It was the technique of equitone. It consisted in maintaining a single level of tone and attitude to the reader throughout the entire composition. (Understanding Media, 206)

1964
As early as 1830 the French poet Lamartine had said, “The book arrives too late,” drawing attention to the fact that the book and the newspaper are quite different forms. (…) The mosaic of the [ newspaper] press manages to effect a complex many-leveled function of group-awareness and participation such as the book has never been able to perform. (Understanding Media, 205, 216)

1964
“depth” means “in interrelation”, not “in isolation”. Depth means insight, not point of view; and insight is a kind of mental involvement in process that makes the content of the item seem quite secondary. Consciousness itself is an inclusive process not at all dependent on content. Consciousness does not postulate consciousness of anything in particular. (Understanding Media, 282-283)

1965
The new stories tend to be much more compressed and on two levels at once, like the sort of Finnegans Wake phrase: “though he might have been more humble, there’s no police like Holmes.”⁸ That kind of compressed double-plot story is a  very interesting development… (Address at Vision 65)

1967
Highly literate people speak on one level, in a monotone. “Good” prose is spoken this way. A [singular] level of form, one plane. You cannot discuss multi-relationships on a single plane, in a single form. That’s why the poets of our time have broken all the planes and sequences, forming a cubist prose. (Hot & Cool Interview with Gerald Stearn)

1967
Freud’s Interpretation of Dreams reveals the amazing power that all people have in their dream life of invention and poetic discovery; that the most ordinary person in his dream life is a tremendous poet. Most Freudians are concerned with the subject-matter of this poetry. That never interested me. I was always fascinated by the amazing ingenuity, symmetry, and inventiveness of the dreamer. We all have these tremendous unused powers which we use surreptitiously. We are afraid to use them in our waking lives. Except the artist. The artist uses in his waking life the powers an ordinary person would use in his dream life. The creative man has his dream life while awake. (…) The dream is a way of processing waking experiences in a pattern which is non-lineal, but multi-leveled. (McLuhan interview with  Gerald Stearn, McLuhan Hot & Cool)

1967
Consciousness (…) is a specialist and fragmentary operation which works by exclusion rather than inclusion. The subconscious by contrast is inclusive rather than exclusive  It accepts all things and all times and all places, and accepts them all-at-once. (The Future of Morality: inner vs outer quest)

1968
The seventeenth-century interassociation of varied levels of fact had begun to appear incompatible with the new science of the time. (Through the Vanishing Point, 10)

1968
Much of A Preface to Chaucer by D. W. Robertson (Princeton University Press, 1962) is concerned with explaining how the world of space and  time in the art of Chaucer is discontinuous and multileveled. For the modern scholar, the discovery of discontinuity creates dismay since it disrupts his ordinary procedures and classifications. Robertson, for example, declares that the principles of conventional philology are quite inadequate to the task of  establishing an encounter with the Medieval habits of multileveled exegesis. (Through the Vanishing Point, 238)

1968
Depth requires perception on many levels and, therefore, an absence of single purpose or direction. (All of the Candidates are Asleep)

1968
The mechanical enthroned the “point of view”, the static position with its vanishing point. The electric age favors a total field approach, a kind of X-ray in depth which not only avoids a point of view but avoids looking at situations from any single level.  (Environment As Programmed Happening)

1968
The same speed of access to many kinds of data has given us the power to X-ray all the cultures and subcultures in the world. We no longer approach them from any point of view or for the purpose of taking a picture of them. The new approach is the X-ray approach of penetration in depth to achieve awareness on many levels at once. It is natural that we should adapt this approach to our own condition. The psychiatrists have done so for the individual, and comparable analysis is now available for the corporate or group condition. (Environment As Programmed Happening)

1968
The simultaneous interrelations between many levels of meaning of the word have to be sacrificed in keeping everything moving on a single plane on one level. (The Medium Is The Massage LP)

1970
L. P. Smith in Words and Idioms draws attention to a mysterious property of language, namely, the ineradicable power of doublets. The Greek word for these structures [is] hendiadys, “one through two”… (From Cliché to Archetype, 108)

1970
consciousness is (…) a multileveled event (From Cliché to Archetype, 117)

1972
How about the adman’s rip-off?  He must move on more than one level in order to obtain the the interplay that involves the public. (‘Introduction’ to Subliminal Seduction)

1974
There was for many centuries [up to the end of the middle ages] a decorum in dress and costume as much as in speech and levels of rhetorical style. The structuralism upon which these distinctions was based was not visual but acoustic, and [when this ended] the same process of levelling in dress or in costume proceeded by the same means as the levelling of rhetorical styles and exegetical levels of interpretation of scripture. Those means were, of course, the advent of [Gutenbergian] technologies which stepped up visual stress to new levels of intensity, just as today the advent of powerful new acoustic structures in the environment have disposed human perception towards an easy understanding and acceptance of complex non-visual structures once more. (The Medieval Environment)

1974
Bacon’s organic approach, I suggest, is derived from the multi-levelled exegesis of the book of nature and Scripture alike. The simultaneity of all levels in ancient grammatica coincides with twentieth century quantum mechanics which is concerned with the physical and chemical bond of nature as the “resonant interval.” The acoustic simultaneity of the new physics co-exists with “synchrony” and structuralism in language and literature and anthropology as understood in Ferdinand de Saussure and Levi-Strauss. (Bacon, Ancient or Modern?)

1979
Contemporary linguistics [ie, Saussure] has recovered the multileveled study of language in our time. (Pound, Eliot, and the Rhetoric of The Waste Land )