In his 1954 lecture, ‘Catholic Humanism and Modern Letters’ (CHML), McLuhan draws an extended parallel between Plato’s cave and the movies. Plato’s allegory presents an “image of human life” where “existence is a kind of cave or cellar on the back wall of which we watch the shadows of real things from the outside world of reality”. And now today, “the dreaming eye of the movie god casting his images on the dark screen corresponds to that image of human life offered to us by Plato in the Republic“. The allegory drawn by Plato and the modern medium both raise fundamental questions concerning the relationship of image and reality, epistemology and ontology. McLuhan proposes to use a comparison of the two to investigate what occurs “in every instant of perception”¹ in “our primary and constant mode of awareness”.²

Plato’s allegory of the cave in the Republic (514a–520a) is unfolded in an exchange recollected by Socrates between himself and Glaucon:

Socrates: Behold human beings living in an underground cave, which has [its] mouth open towards the light and [reaches deep into the earth]; here they have been from their childhood, and have their legs and necks chained so that they cannot move, and can only see before them, being prevented by the chains from turning round their heads. Above and behind them a fire is blazing (…) and between the fire and the prisoners there is a raised [walk]way; and you will see, if you look, a low wall built along the [walk]way, like the screen which marionette players have in front of them, over which they show their puppets. (…)
And do you see, I said, men passing along [the walkway behind] the wall carrying [figurative objects above them] — all sorts of vessels, and statues and figures of animals made of wood and stone and various materials, which appear over the wall [like the puppets in a marionette theatre]? (…)
Glaucon: You have shown me a strange image, and they are strange prisoners.
Socrates: Like ourselves, I replied; and they see only their own shadows, or the shadows of one another, which the fire throws on the opposite wall of the cave?
Glaucon: True, he said; how could they see anything but the shadows if they were never allowed to move their heads?
Socrates: And of the objects which are being carried [along the walkway], in like manner they would only see the shadows? (…)
And if they were able to converse with one another [about the shadow images before them], would they not suppose that they were [discussing real things] ? (…)
To them, I said, the truth would be literally nothing but the shadows of the [figures carried along the walkway]. (…)
And now look again, and see what will naturally follow if the prisoners are released and disabused of their error. At first, when any of them is liberated and compelled suddenly to stand up and turn his neck round and walk and look towards the light [of the fire], he will suffer sharp pains; the glare will distress him, and he will be unable to see the realities of [the puppet figures of] which in his former state he had seen [only] the shadows; and then conceive someone saying to him, that what he saw before was an illusion, but that now, when he is approaching nearer to [the real] being [of the figures] and [since] his eye is turned towards [their] more real existence, he has a clearer vision — what will be his reply? And you may further imagine that his instructor is pointing to the [figure] objects as they pass [above the wall of the walkway] and requiring him to name them — will he not be perplexed? Will he not fancy that the shadows which he formerly saw were [more real and] truer than the objects which are now shown to him? (…)
And if he is compelled to look straight at the light [of the fire], will he not have a pain in his eyes which will make him turn away [back to] the [shadow] objects of vision which he can see [without pain], and which he will conceive to be in reality clearer than the things which are now being shown to him [in the fire’s light]? (…)
And suppose, once more, that he is reluctantly dragged up [the cave over] a steep and rugged ascent, and held fast until he’s forced into [the outside world and into] the presence of the sun itself, is he not likely to be [even more] pained and irritated? When he approaches the [sun’s] light his eyes will be dazzled, and he will not be able to see anything at all of what [is in the outside world]. (…)
He will require [time] to grow accustomed to the sight of the upper world. And first he will see [only] the shadows [of things] best, next the reflections of men and other objects in water, and [finally] the objects themselves; then he will gaze upon the light of the moon and the stars and the spangled heaven; and [at first] he will see the sky and the stars by night better than the sun or the light of the sun by day. (…)
Last of all he will be able to see the sun, and not mere reflections of it in water, but he will see it in its own proper place, and not in another; and he will contemplate it as it is. (…)
He will then proceed to argue that this is [the power] which gives [us] the seasons and the years, and is the guardian of all that is in the visible world, and in a certain way the cause of all things (..)
And when he remembers his old habitation [in the cave], and the [accepted] wisdom of the cave and [of] his fellow-prisoners, do you not suppose that he would [rejoice] in the change [he has undergone], and pity them? (…)
And if [the prisoners] were in the habit of conferring honors among themselves on those who were quickest to observe the [order of the] passing shadow [images] and to remark which of them [regularly] went before, and which followed after, and which were [regularly] together [with one another]; and who were therefore best able to draw conclusions as to the future [order of the shadow images from these observations], do you think that he would care for such honors and glories, or envy the possessors of them? (…)
Imagine once more, I said, such a one coming suddenly out of the sun to be placed again in his old situation [in the cave]; would he not be certain to have his eyes full of darkness? (…)
And if there were a contest, and he had to compete in [investigating] the shadow [images] with the prisoners who had never moved out of the cave, while his sight was still weak, and before his eyes had become steady [in the dark once more](…), would he not be ridiculous? Men would say of him that he went up [in the cave] and [when] he came down [again, he was] without [the use of] his eyes; and that it was [therefore far] better not even to think of ascending [which had left him without his sight in this way]; and if anyone tried to loose another [prisoner from his chains] and lead him up to the light (…) they would put [the one attempting to free the prisoner] to death [as happened to Socrates³].⁴

In further Plato’s Cave posts, the full CHML passage will be given, and analyzed at length, in which McLuhan discusses Plato’s allegory in relation to the movies. Here only a single sentence will be singled out for particular notice:

the mechanical medium [the movie] has tended to provide merely a dream world which is a substitute for reality rather than a means of proving reality. (Emphasis added)

‘A means of proving reality’ here may well be a typo for ‘a means of prov(id)ing reality’:⁵

the mechanical medium [the movie] has tended to provide merely a dream world which is a substitute for reality rather than a means of providing reality. (Emphasis added)

‘Proving’ is not impossible here since McLuhan was hardly allergic to unusual constructions and the related (originally identical doublet) word ‘probing‘ was a favorite of his. Moreover, it is exactly the central point of CHML that, properly considerered, “modern letters” and modern science may be taken as “proving reality” (rather than being ontologically neutral).⁶

However, typos are common in McLuhan’s work (he notoriously refused to proofread his texts) and ‘providing’ is a recurrent term in CHML. In fact it appears multiple times in this same sentence.⁷

Further, the word ‘pro-vide’ itself raises the fundamental matter at stake here, namely, the riddle of what is before (‘pro’) our vision (‘vide’) in space as the question of what is before our vision in time.⁸ 

The great issue for McLuhan both in Plato’s cave and in the movies is exactly whether the images seen in them present “a dream world” which is taken to be real (“a substitute for reality”) or one which is known to result from a particular “means”, or medium, which provides that particular sort of reality (“a means of prov(id)ing reality”).

Between the two, the nature of time is at stake. The first lives exclusively in diachronic time and therefore cannot know its experience as an effect of a prior cause. Its notion of cause and effect is such that what is experienced ‘first’ is cause and what is experienced ‘later’ is effect. In fundamental contrast, the second understands that what is experienced ‘first’ may be the effect of what is experienced ‘later’ as cause.⁹ In the allegory of the cave, the prisoner who is loosed from his chains and experiences the outside world comes to learn later the cause of his earlier notions of truth and reality now considered as effect.¹⁰

In the first case, the medium is unknown, or at least unconsidered, and it is this lack of consideration which then chains human “prisoners” to false ideas of reality and of truth. In Plato’s cave, the prisoners do not know that they are in a cave, they do not know that are prisoners, they do not know that their light comes from a fire, they do not know that the objects they see are shadows, etc etc.  They do not know the medium of their vision any more than fish are aware of water. The thing that is most obvious to their situation, seen from the outside, their “strange” environment, is oblivious to them from the inside.

In the second case, the medium is known. In Plato’s allegory the prisoner who is loosed to leave the cave learns the circumstances which previously determined his vision and his corresponding ideas of reality and truth. He now knows that these were only one “means [among many] of prov(id)ing reality”. He now knows that the medium is the message.