The basis of all paradox, Christian and secular, is to be found in the sixth book of the Physics of Aristotle, to which Aquinas refers in his Summa Theologica I.II.q 113.a.7, ad quintum. The question for Aquinas is whether justification by faith occurs instantly or gradually. Aquinas says it occurs instantly because — ­here he appeals to Aristotle’s Physics  — “the whole preceding time during which anything moves towards its form, it is under the opposite form.” (From Cliché to Archetype, 1970).

McLuhan, at least from the time of his graduate studies around 1940, was interested in Seneca and the question of how learning eventuates. But this (as McLuhan himself came to specify only in the late 1950s) is the same question as: what is communication?

Here is McLuhan on Seneca in chronological order with added bold and commentary in footnotes.

1943
The war between the dialecticians and rhetoricians began as soon as the Sophists attempted to make dialectics subordinate to the art of persuasion. Plato and Aristotle were the greatest enemies of the rhetoricians, not so much in rejecting rhetoric, as in asserting that as an art it had no power to control dialectics.  The Stoics, however, are the main defenders of dialectics against rhetoric after [Plato and] Aristotle.¹ It was they who made Cicero very uncomfortable on many occasions, and against them he, as rhetorician, directs the main force of his attack. It is in terms of the Stoic contempt of persuasion [rhetoric] and their love of cryptic and compressed utterance that one is  able to understand the ancient rivalry between the Attic and Asiatic styles — later, between the Senecans and Ciceronians. The war between these literary camps is basically the opposition between dialectics and rhetoric to control the modes of literary composition; and the ramifications of this opposition stretch into the realms of ethics and politics, both in Antiquity and in the Renaissance. (The Place Of Thomas Nashe In The Learning Of His Time)

1943
Donne is quite explicit about his rhetorical aims in preaching. His intention was to arrange his rhetorical effects in such a way as “to trouble the understanding, to displace, and discompose and disorder the judgement (…) or to empty it of former apprehensions, and to shake beliefe, with which it had possessed it self before, and then, when it is thus melted to poure it into new molds, when it is thus mollified, to stamp and imprint new formes, new images, new opinions in it.” Donne is here stating the Attic or anti-Ciceronian concept of style espoused by the Senecans. His words describe the aims set themselves by Montaigne and Bacon in their essays. In The Advancement Bacon contrasts the two modes of delivering knowledge as the modes of aphorism and orderly method: “But the writing in aphorisms hath many excellent virtues, whereto the writing in Method doth not approach. For first, it trieth the writer, whether he be superficial or solid: for Aphorism, except they should be ridiculous, cannot be made but of the pith and heart of sciences; for discourse illustration is cut off: recitals of examples are cut off; discourse of connection and order cut off; descriptions of practice are cut off (…) And lastly, Aphorisms, representing a knowledge broken do invite men to inquire farther; whereas Methods, carrying the show of a total do secure men, as if they were at farthest.” Both Montaigne and Bacon made compromises, gradually admitting examples, authorities, and descriptions, but persisting in their original intention of employing an aphoristic style in order to dislocate the mind from its customary courses. (The Place Of Thomas Nashe In The Learning Of His Time)

1943
It is easy to see how the aphorism was indispensable to this mode of composition employed by Bacon, Burton, Donne, and Browne. It is equally important to recognize that a statecraft, or theory of politics, as well as rhetoric, was the mainstay of the Attic style.²  As [M.W.] Croll³ says: “The negligence of the anti-Ciceronian masters, their disdain of revision, their dependence upon casual and emergent devices of construction, might sometimes be mistaken for mere indifference to art or contempt of form⁴ (…) Yet even their extravagances are purposive, and express a creed that is at the same time philosophical and artistic. Their purpose was to portray, not a thought, but a mind thinking, or, in Pascal’s words, la peinture de la pensée“. Thus the ‘cutted period,’ asymmetry of members, sudden shifts from plain to metaphorical statement, or from one metaphor to another, is the result of a style “always tending toward the aphorism, or pensée, as its ideal form“.⁵ In brief, it is a Senecan style. (The Place Of Thomas Nashe In The Learning Of His Time)

1944
Seneca was for Roger [Bacon], and many others, a Christian worthy, and the relative claims of his eloquence and that of Cicero was a dispute which uninterruptedly split the learned world from the beginning until after the time of Montaigne and [Francis] Bacon. (Francis Bacon’s Patristic Inheritance)⁶

1944
Elocution, like invention, is of two kinds: [according to Francis Bacon] “it is either magistral or initiative. (…) I call that doctrine initiative (borrowing the term from the sacred ceremonies) which discloses and lays bare the very mysteries of the sciences.⁷ The magistral method teaches; the initiative intimates. The magistral requires that what is told should be believed; the initiative [requires] that it should be examined. The one transmits knowledge to the crowd of learners; the other to the sons, as it were, of science.” In a word, the one style is Ciceronian, the other Senecan. (Francis Bacon’s Patristic Inheritance)

1951
Landscape offered several attractive advantages to the poets of the mid-eighteenth century. It meant for one thing an extension of the Baroque interest in la peinture de la pensée, which the study of Seneca had suggested to Montaigne and Bacon and Browne — an interest which reached a maximal development, so far as the technique of direct statement permitted, in Pascal, Racine, and Alexander Pope. Pope especially deserves study from this point of view since he first developed the couplet to do the complex work of the double-plot of the Elizabethans. He discovered how to make a couplet achieve a symbolic vision. That is, to effect an instant of inclusive consciousness by the juxtaposition without copula of diverse and even paradoxical situations or states of mind.⁸ (Tennyson and Picturesque Poetry)

1952
The conflicting claims of dialectic and rhetoric or private and public communication account for a good deal of subsequent intellectual and social history. The Roman world divided the dispute in accordance with the position of Seneca and of Cicero, and the mediaeval world opposed the methods of study and teaching of the [Ciceronian] Fathers and the [Senecan] Schoolmen.⁹ (Technology and Political Change)

1953
Because the function of the exegete is to reveal the hidden and the obscure, he naturally resorts to those forms of expression which arrest the flow of the mind by sudden turns, or dislocate it from its usual channels. (…) By juxtaposing well-known styles [from classical rhetoric] with contemporary themes and controversies, Lyly and Nashe were exercising the art of the continuous parallel so strikingly used in [Joyce’s] Ulysses and in the Senecanism of [Eliot’s] Gerontion and Sweeney Agonistes.¹⁰ (From Eliot to Seneca)

1953
The Church Fathers are always close to Seneca for the same reason they are close to Pliny. Seneca provided the stylistic means of psychological manipulation of the inner world [just as]¹¹ Pliny exercised the same effects via the objects of the outer world. Montaigne, interested above all in arresting and painting thought, uses the quick conversational turns of Senecan style and the wide variety of stances provided by [Pliny’s]¹² world of natural history to snap-shot the various postures of the mind. (From Eliot to Seneca)

1953
The natural and age-old antipathy of Senecan and Ciceronian is rooted in diversity of aim and method in communication. The Senecan cares only to reveal the thing. He is an instrument to be set aside the moment that the reader has been helped to see. (From Eliot to Seneca)

1953
The [Senecan] circuit represents not a narratio or a record of events, but the stages of the learning process.¹³ The discontinuities of Senecan style, whether in Bacon’s Essays or Mr. Eliot’s poetry, are not attempts to take the reader by the hand or to unfold a tale, but attempts to reveal exactly discriminated states of mind by devices geared to inner vision. The Ciceronian, however, is engaged not in revelation but self-expression. He takes up the task not of discovery and learning but of transmission and accumulation of data, and the inculcation of moral attitudes. (From Eliot to Seneca)

1953
Bacon upon occasion used both [Ciceronian and Senecan] styles and so does Mr. Eliot. Quarrels between Senecans and Ciceronians are inevitably the result of the triumph of specialized temperament over general intelligence. (From Eliot to Seneca) 

1953
The Senecan schools of declamation in the Roman world elaborated all those terms and procedures which the twelfth-century Senecans revived and elaborated. The Sic et Non of Abelard, like the antitheta of Bacon, is a technique of juxtaposition of texts for the purpose of sudden illumination. Scholasticism was Senecan in origin and temper, and opposed to the Ciceronian humanism of medieval philology and pedagogy. This perspective would have helped Professor Williamson [in his Senecan Amble] to locate the line of wit.¹⁴ (From Eliot to Seneca)

1953
Seen in the light of its close historical relation with scholasticism, the [seemingly inexplicable] Senecan link with scientific method, on one hand, and with Puritan theological procedure, on the other, becomes explicable. (From Eliot to Seneca) 

1953
It was the distinction of Pope to have perfected the Senecan essay in verse as a precise instrument of dramatic moral dissection. The return to Senecan style in our time has been made possible by means of the technique of the interior landscape in poetry. The great impetus which Newton gave to the elaboration of external landscape lasted until this century. But the Senecal world, concerned with the postures of mind and the figures on the inner psychological stage, was mainly suppressed by Newtonian physics and optics. There was something revolutionary, therefore, about Mr. Eliot’s directing his exegesis to the Senecal techniques of the Elizabethan and Jacobean drama and his incorporating these via Laforgue and Rimbaud in his early poems. (From Eliot to Seneca) 

1953
In rewriting my doctoral dissertation I am going to include a history of Senecanism as the opponent of Ciceronianism. (…) Seneca is the way of gnosis. Cicero of expression. Senecans stress connatural [innate], irrational [not continuous] knowing via the passions. (McLuhan letter to Eric Voegelin)¹⁵

1953
You know my theory of the origin of the technique of scholastic philosophy out of Senecan antitheta. (McLuhan letter to Archie Malloch)

1962
Scholasticism, like Senecanism, was directly related to the oral traditions of aphoristic learning. When it is understood how entirely oral [scholastic] thesis defenses were, it is easier to see why the students of such arts would need to have memories furnished with a large repertory of aphorisms and sententiae. This is a factor in the prevalence of Senecan stylistic in later Roman times and for the long association of Senecan style with “scientific method” both in the middle ages and in the Renaissance. For Francis Bacon, as much as for Abelard, “writing in aphorisms” rather than in “methods” was the difference between keen analysis and mere public persuasion. In The Advancement of Learning, which is itself shaped as a public oration, Bacon prefers, on intellectual grounds, the scholastic technique of aphorism to the Ciceronian method of explicit spelling out of information in the form of continuous prose. (…) We find it hard to grasp that the Senecan Francis Bacon was in many respects a schoolman. (Gutenberg Galaxy)

1962
Attention to Senecanism and scholasticism in ancient Rome will help [the reader] to understand how oral tradition in Western literature is transmitted by the Senecan vogue,¹⁶ and was gradually obliterated by the printed page in the later eighteenth century. The paradox that Senecanism is both highbrow in medieval scholasticism and lowbrow in the Elizabethan popular drama will be found to be resolved by this oral factor. But for Montaigne, as for Burton, Bacon, and Browne, there was no enigma. Senecan antithesis and “amble” (as described in Senecan Amble by George Williamson) 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)