the (…) way in which the lines of force in any medium are structured. (McLuhan to Harry Skornia, 25 January 1960)¹

When stress moves from product to process… (McLuhan to Claude Bissell, May 6, 1960)²

Understanding Media [= Report on Project in Understanding New Media] postulates the basic hypothesis that any means of codification of experience in terms of any sense whatever inevitably transforms the ratio among the other senses and thereby alters patterns of thought, feeling, and action. (‘Title VII Research Abstract’, 1961)³  

McLuhan experienced enough self-styled breakthroughs in his career that he sometimes complained that he didn’t have time to write them down.  The single most important one of these occurred in January 1960:

Early in 1960 it dawned on me that the sensory impression proffered by a medium like movie or radio, was not the sensory effect obtained.⁴ Radio, for example, has an intense visual effect on listeners. But then there is the telephone which also proffers an auditory impression, but has no visual effect. In the same way television is watched but has a very different effect from movies. These observations led to a series of studies of the media, and to the discovery of basic laws concerning the sensory effects of various media. These will be found in this report.  In 1915 Heinrich Wölfflin published his Principles of Art History which has since then revolutionized the study of many matters besides art. His entire approach confirms what I discovered about media: “the effect is the thing that counts, not the sensuous facts“⁵… (Report on the Project in Understanding New Media)

The last few days have seen a major breakthrough in media study. Working with the fact that each medium embodies one or more of the human senses, it struck me that we are impelled in perceiving each medium to complete the scale or spectrum of our sensorium. So that, radio impels us to provide a visual world moment by moment, and photography, which is so adequate in visual terms, compels us to complete the tactual and kinesthetic part of the sensorium. Thus the degree of sensuous completion is one way in which the lines of force in any medium are structured. (McLuhan to Harry Skornia, 25 January 1960)⁶

The break-through in media study has come at last, and it can be stated as the principle of complementarity: that the structural impact of any situation is subjectively completed as to the cycle of the senses. (McLuhan to Bernard Muller-Thym, February 19th, 1960)⁷

As far as the project goes, rather large developments and discoveries have occurred in the last few weeks which will enable me to complete it in a very satisfactory manner while, at the same time, opening a new phase of media study… (McLuhan to John Wain, March 11, 1960)⁸

Some large breakthroughs have occurred in communication study…⁹ (McLuhan to Peter Drucker, April 18, 1960)¹⁰

At first following Innis, Havelock and Richards in the late 1940s¹¹, and then working with the Explorations seminar group in the middle 1950s, McLuhan by 1960 had considered for more than a decade how media shape experience through the manipulation of the senses — particularly the ear in illiterate cultures and the eye in literate ones. But now, in January 1960, he came to the idea that media — and therefore all human experience (since all human experience is media-ted at the very least by language and culture) — that media and all human experience might be characterized by specifiable structure.¹² Furthermore, he saw that such a specifiable structure, once tentatively accepted for collective investigation, could represent the “opening [of] a new phase of media study” leading to “the discovery of basic laws”.

He immediately saw that collective study along these lines, with the promise of the sorts of progressive and sometimes revolutionary findings that other sciences such as chemistry and genetics had made once an elementary structure had been identified for common focus in their fields, could have enormous effect on the great questions of the contemporary world. And, given the state of the world with the threat of nuclear weapons in war, of pervasive automation in the economy, and environmental disaster in the biosphere, this effect could hardly be for the worse. Indeed, the accumulative result of the new investigation was its promise finally to lift the automata-like slavery of humans to the media control of their experience — which was leading the planet into multiple disasters.

Once he began looking at media as structures, McLuhan saw various possibilities for scientific investigation. For example, he saw that different media stimulated the human sensorium with different intensities: what he called High Definition (HD) and Low Definition (LD). Already in 1960 this would lead him to the famous typology of hot (HD) and cool (LD) media. Then, given some such input, he hypothesized that “we are impelled in perceiving each medium to complete the scale or spectrum of our sensorium”. The initial idea (never fulfilled in practice, but perhaps never yet fully appreciated) was that it might be possible to establish that the ratio between the sensory input of a medium and the inverse (high response to low input and vice versa) ‘subjective completion’ (SC)¹³ of a perceiver would maintain itself according to some dynamic constant or, at least, might prove to have predictable action somewhat as valence does in chemistry. Comparable to the action of valence, the hypothetical goal of all experience would be to convert an unstable initial situation into a subsequent stable one.¹⁴ On this model, human being would ceaselessly function as a kind of gyroscope working to keep the changing inputs of experience in balance.  As McLuhan wrote to Jackie Tyrwhitt on December 23, 1960:

Is not this the problem that we have now to face in the management of inner and outer space, [a question] not [of] fixed but [of] ever new-made ratios, shifting always to maintain a maximal focal point of consciousness?¹⁵

Or again in the 1961 ‘Care and Feeding of Communication Innovation’:

the senses never operate in isolation [from one another]. If one sense is suppressed, the other senses compensate in various ways in order to maintain that steady ratio among the senses which is the norm of human consciousness. If one sense is [relatively] isolated by stress or intensity we are in the state of hypnosis at once. Pushed a bit further, the [more extreme] isolation of [a] sense [relative to the others] leads swiftly to insanity.

This implicated the further idea that scientific investigation might focus on the senses themselves in their attempt “to maintain that steady ratio among the senses which is the norm of human consciousness“. This facility dynamically seeking sensory stability was called by McLuhan ‘tactility’ — or ‘kinesthesia’ or ‘synesthesia’ or ‘equilibrium’ or ‘the sensus communis‘ — and he postulated that it could be defined in terms of the ratio between the visual and the aural:

There are only two basic extreme forms of human organization. They have innumerable variants or “parti-colored” forms. The extreme forms are the (…) eye and ear… (Take Today, 22)

The idea was not that the eye and the ear ever function aside from the ‘synesthesia’ of the five senses, but that they have a specialized role in the investigation of human experience comparable to the specialized role of the electron (which in practice never functions aside from a host of other particles in the atom) in the investigations of chemistry (particularly in regard to valence). Moreover, the visual and the aural were to be defined, not in terms of either sent or received sense data — “the sensory impression” — but in terms of “the effect”.¹⁶ And the effects of media were the “variants” of time-space experience: 

each sense actually makes its own space with its own distinctive perceptual structure. (Take Today, 137)

The elements of experience would then be the plenary spectrum of time-space configurations specifiable as variations of the basic ear-eye ratio. The hope would be that they would prove as fertile for new discoveries, and indeed even for whole new sub-sciences, as was the case following the definition of elementary structures in chemistry and genetics. And this, in turn, might provide an answer to the “threat to continued existence and to sanity”¹⁷ posed to the planet, then and now, by the limitless assertion of unconsidered assumptions.¹⁸