In 1951 “arrest in time” became a decisive theme in McLuhan’s work that he would continue to investigate for the remaining three decades of his career. Perhaps no other of his myriad ‘discoveries’ was more important for his project. 

Below are some of his “arrest” passages in chronological order. Their take-off point may be seen in McLuhan’s letter to Harold Innis from March 14, 1951:¹

One major discovery of the symbolists which had the greatest importance for subsequent investigation was their notion of the learning process as a labyrinth of the senses and faculties whose retracing provided the key to all arts and sciences (…) Retracing becomes in modern historical scholarship the technique of reconstruction.

McLuhan soon saw that the key to such retracing and reconstruction was ‘arrest’. He seems to have come along the way of this insight by considering picturesque poetry as an attempt to effect an arrested “aesthetic moment” and then to have then seen, apparently through Joyce’s Stephen Hero, that such poetic arrest was a replay or retrieval of the arrest that already operates both in “every moment of human awareness” and in all language use as a kind of “stuttering”. So conceived, ‘arrest’ implicated a special understanding of space — “the gap where the action is” — and of time — “a moment in and out of time”.² “This peculiar fusion of the [ordinary] cognitive and the [extraordinary] creative by an act of retracing the stages of apprehension was arrived at by Joyce as a result of the prior discovery [of the importance of] the technique of fission [for] the moment of aesthetic awareness. (…) In art as in physics fission preceded fusion.”³

The Aesthetic Moment in Landscape Poetry, 1951
It was partly to Schopenhauer that the symbolists owed their peculiar insistence on aesthetic experience⁴ as an arrested moment, a moment in and out of time,⁵ of intellectual emotion⁶ for which, in their poems, they sought the art formula by retracing the stages of apprehension which led to this moment.

The Aesthetic Moment in Landscape Poetry, 1951
The aesthetic moment was recognized as an experience of arrest and detachment.⁷

The Aesthetic Moment in Landscape Poetry, 1951
Helped by Rimbaud and Mallarmé, Joyce arrived quickly at the formula of the aesthetic moment and its attendant landscape as consisting in a retracing of the stages of ordinary apprehension. The poetic process he discovered and states in Stephen Hero is the experience of ordinary cognition, but it is that labyrinth reversed, retraced, and hence epiphanized. The moment of arrested cognition achieves at once its stasis and epiphany as a result of the reconstruction of the stages of ordinary apprehension. And every moment of cognition is thus a Beatrician [= epiphanized or sacramental] moment when rendered lucid by a retracing of its labyrinth. (…) This secret consists in nothing less than a fusion of the learning and the creative processes⁸ 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 [= arrest] of the moment of aesthetic awareness. (…) In art as in physics fission preceded fusion.⁹ 

McLuhan to Ezra Pound, July 16, 1952¹⁰
I’m writing a book on “The End of the Gutenberg Era”. Main sections: The Inventions of Writing [&] Alphabet (Transfer of auditory to visual; Arrest for contemplation of thought and cognitive process; Permits overthrow of sophist-rhetoric-oral tradition)¹¹

Wyndham Lewis: His Theory of Art and Communication, 1953
“Plato’s theory of Ideas institutes a gigantic effort to establish the mystic doctrine upon an intellectual basis.”¹²(…) From this point of view Greek Philosophy and science were a means of arresting the wheel of existence or of delivering us from the time mechanism of existence.¹³

James Joyce: Trivial and Quadrivial, 1953
The idea of speech as stuttering, as arrested gesture (…) is basic to the Wake and serves to illustrate the profundity of the traditional philological doctrine in Joyce.

Catholic Humanism and Modern Letters, 1954
Impressionism and symbolism alike insisted on attention to process in preference to personal self-expression. Self-effacement and patient watchfulness preceded the discovery of the creative process. Poets and artists literally turned their own psyches into laboratories where they practised the most austere experiments in total disregard of their personal happiness. Gradually it dawned on Mallarmé that pure poetry was (…) a poetry which would have as its theme the poetic process itself. Henceforth the subject and framework of a poem would be the retracing of a moment of perception. For some of the Romantic poets the doctrine of the aesthetic moment as a moment out of time — a moment of arrested consciousness — had seemed the key to all poetry. The pre-Raphaelites had pushed this doctrine as far as they could. But Mallarmé saw deeper and Joyce saw the rest. Joyce it was who saw that Aquinas had the final answer sought by Mallarmé.  The rational notes of beauty, integrity, consonance, and claritas traced by St. Thomas were actual stages of apprehension in every moment of human awareness. And so we arrive at the paradox of this most esoteric of all art doctrines, namely that the most poetic thing in the world is the most ordinary human consciousness.

Catholic Humanism and Modern Letters, 1954
It would seem that the poet differs from other men only in his conscious ability to arrest the intake of experience and to reverse the flow. By this means he is able to externalize in a work the actual process by which each of us in perception or cognition incarnates the external world of experience. But every word uttered by man requires a large measure of the poetic ability.

Coleridge As Artist, 1957
Poe put crime detection on a scientific basis by bringing into play the poetic process of retracing the stages of human apprehension [in general]. (…) And this process of arrest and retracing (…) provides the very technique of empathy¹⁴ which permits intimate insight into the processes and impulses behind products utterly alien to our own immediate experience.¹⁵

Coleridge As Artist, 1957
the Senecans had (…) literary techniques for arresting and projecting some phase of the human mind: to arrest in order to project, and to project in order to contemplate. Like the inventors of cinema at the beginning of this century they hit upon the technique of stylistic discontinuity as a means of analyzing or arresting a moment of consciousness.

Coleridge As Artist, 1957
“Calm is all nature as a resting wheel.” That is the master vision of all those “spots of time” for which Wordsworth painfully sought the precise objective correlative in carefully wrought landscapes. It is the key to all his lyrics and even to The Prelude, which in order to follow his process of enlightenment has to arrest for contemplation the entire movement of his mind from youth to age.

Coleridge As Artist, 1957
As poetic practitioners Wordsworth and Coleridge were in agreement (…) that poetry was concerned with the rendering of an instant of arrested awareness which freed the mind from the clogs of habitual perception.

Coleridge As Artist, 1957
Moments of insight in Wordsworth’s poetry are explicitly associated with an experience of an arrest in time.¹⁶ 

Coleridge As Artist, 1957
Suspense [in Byron] is not for thrill but for arrest of movement for contemplation, and to create one of those “spots in time” which permit a flash of intuitive wisdom.