The doctrine of names is, of course, the doctrine of essence and not a naïve notion of oral terminology. (The Place of Thomas Nashe in the Learning of His Time)¹

Just as language offers an extensive and complex apprehension of the structure of beings, so that faculty which produced this state of language is perpetually operative — an intuitive perception of essentials. (The Place of Thomas Nashe in the Learning of His Time)²

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Here in chronological order are McLuhan’s thoughts on the Cratylus of Plato and its “doctrine of names” (with commentary in footnotes):

The Place of Thomas Nashe in the Learning of His Time, 1943:³
In the dialogue named for Cratylus, the follower of Heraclitus, Plato has this exchange of arguments between Socrates and Cratylus: Socrates: But if these things are only to be known through names, how can we suppose that the givers of names had knowledge, or were legislators before there were names at all, and therefore before they could have known them?Cratylus: I believe, Socrates, the true account of the matter to be, that a power more than human gave things their first names, and that the names which were thus given are necessarily their true names. Obviously, with this kind of importance associated with the names of things, and of gods, heroes, and legendary beings, etymology would be a main source of scientific and moral enlightenment. And such was the case. The prolific labors of the etymologists reflected in Plato’s Cratylus, but begun centuries before and continued until the seventeenth century, are as much the concern of the historian of philosophy and of science as of the historian of letters and culture. Indeed, it was not only in antiquity but until the Cartesian revolution that language was viewed as simultaneously linking and harmonizing all the intellectual and physical functions of men and of the physical world as well. At any time from Plato to Francis Bacon the statement of Cratylus would have made sense, and would have evoked respect.

The Place of Thomas Nashe in the Learning of His Time, 1943:⁴
Plato’s Cratylus broaches the question of analogy and anomaly in such a way as to indicate that their dispute was of ancient⁵ origin even in his day, but the issues [between analogy and anomaly]⁶, of course, are drawn on a plane loftier than that of [linguistic] conjugations and declensions. Socrates refutes the superficial anomalist doctrine of Hermogenes at great length. Hermogenes says, ‘I have often talked over this  matter, both with Cratylus and others, and cannot convince myself that there is any principle of correctness in names other than convention and agreement.’ Socrates replies that ‘I should say that this giving of names can be no such light matter as you fancy (…) and [that] Cratylus is right in saying that things have names by nature, and that not every man is an artificer of names; but he only who looks to the name which each thing by nature has, and is, will be able to express the ideal forms of things in letters and syllables.’⁷ The general incredulity concerning Socrates’ seriousness in this dialogue is an adequate measure of the modern failure to apprehend the nature of grammar in the ancient and medieval worlds; and much of Plato’s power over St. Augustine and the medieval mind [generally] is owing to his great (…)⁸ respect for the method of grammar in philosophy.

Medieval Grammar as the Basis of Bacon’s Novum Organum, 1944:
One obvious consequence of the doctrine of the Logos is seen in the Cratylus, named for the famous grammarian who was Plato’s teacher. Socrates concurs in Cratylus’ statement that “a power more than human gave things their first names, and (…) the names which were thus given were necessarily their true names.” The dialogue is then given over to the consideration of essence and the basic nature of things by means of the grammatical arts of allegory and etymology. 

Medieval Grammar as the Basis of Bacon’s Novum Organum, 1944
Bacon, like the Stoics, was an analogist, though a cautious one. That is, he held the ancient doctrine (…) of the Cratylus of Plato. An understanding of the great historical dispute waged for many centuries between the analogists and the anomalists is basic to an understanding of ancient, medieval, and Renaissance culture. 

James Joyce: Trivial and Quadrivial, 1953
By 1885 Mallarmé had formulated and utilized in his poetry these concepts about the nature of language uniting science and philology, which nowadays are known as “metalinguistics.” However, these views of language were commonplaces to Cratylus, Varro, and Philo Judaeus. They were familiar to the Church Fathers, and underlay the major schools of scriptural exegesis. If “four-Ievel exegesis” is back in favor again as the staple of the “new criticism”, it is because the poetic objects which have been made since 1880 frequently require such techniques for their elucidation. 

The Little Epic, late 1950s⁹
Language itself and every department of human activity would in this view be a long succession of “momentary deities” or epiphanies.¹⁰ And such indeed is the view put forward in the Cratylus of Plato: “I believe, Socrates, the true account of the matter to be, that a power more than human gave things their first names, and that the names which are thus given are necessarily their true names.” In this way etymology becomes a method of science and theology. William Wordsworth called these momentary deities “spots of time”, Hopkins called them “inscapes”¹¹, and Browning built his entire work on the same concept of the esthetic of the “eternal moment”.

The Gutenberg Galaxy
Cratylus: I believe, Socrates, the true account of the matter to be, that a power more than human gave things their first names, and that the names which were thus given are necessarily their true names. This view of Cratylus was the basis of most language study until the Renaissance. It is rooted in the old oral “magic” of the “momentary deity”¹² kind such as is favoured again today for various reasons. (27-28)

McLuhan to Tom Wolfe, October 25, 1965 (Letters, 326)
Plato’s Cratylus presents a theory of language as the key to an inclusive consciousness of human culture much in the style of Finnegans Wake.