Because time is plural for McLuhan as times, and because everything is double, or at least double, words and phrases like ‘the past’, ‘history’, ‘déjà vu‘, ‘obsolescence’, ‘the old’, etc, carry complex meanings in his work. Passages like the following must therefore be read slowly and, so to say, both vertically and horizontally. A vertical reading of these words and phrases points to “another existence” in the realm of the spectrum of sensory thresholds from which synchronic ‘past’ or ‘déjà vu‘ we have come to our present experience.

When a new environment forms, we see the old one as if we lived in a world of the déjà vu. This was, of course, Plato’s theory of knowledge, that it was a form of recognition of that which we had known in another existence.  Much learning theory still accepts this illusion as a warranty that we must learn by going from the familiar to the unfamiliar. Yet this strategy merely ensures that whenever we encounter the unfamiliar, we will translate it into something we already know. It is this that seems to make the present almost impossible to apprehend in any period or culture. It was James Joyce in Finnegans Wake who demonstrated that the way to overcome the fear of the present, and of innovation in general, is to make an inventory of all the effects of the new thing as it encounters all the older forms of the society. Failure to make this inventory results in the use of the present as a nostalgic mirror of the past. (The Future of Morality: inner vs outer quest, 1967)

Strangely running them together, McLuhan discusses déjà vu in this passage in the two radically different ways of the vertical and the horizontal. He first mentions Plato’s theory of recollection according to which learning is achieved through the activation of the forgotten memory of what has been known before. But this is not a ‘before’ in chronological time or chronological sequence. It is not, like the second sort of déjà vu, an “illusion” which merely replicates the past horizontally and makes “the present almost impossible to apprehend” and could never result in the creation or recognition of “innovation”. Instead, this sort of Platonic déjà vu is exactly what enables innovation, and the apprehension of innovation, through a questioning of the assumptions of the present.  Assumptions are active in the present, but are not constant; questioning them requires a vertical descent into the time and space of “another existence” where assumptions are arrayed, decided, maintained and rejected.¹ This sort of déjà vu, so far from translating the new into the old, and the unfamiliar into the familiar, effects the transformation or rebirth of experience through which, alone, innovation can come to light.

McLuhan touched on this sort of rebirth experience that gives access to the “totally different” in his 1972 interview with L’Express:

the key is that they [the young] return to a primitive existence, in which life is reduced to nothing, and they no longer have any kind of identity. They reject their own identity, and become no-one. (…) It is liberation, but when it is total liberation, it is like death. We all know the reincarnation thesis: we are freed from our own body; we can disappear right now and come back totally different next time. This is what we have reached.

In passages from this same time, McLuhan emphasized the first, vertical or “deep”, sense of déjà vu and again brought reincarnation into this context:

Is the déjà vu phenomenon, i.e. ‘I’ve been here before’, exotic with the ‘man of letters’, and normal and un-noticed by non-literate man?  If so it could account for the deep, reincarnational or déjà vu sense of the non-literate societies. The sensation itself may result from situations of deep sensuous involvement, natural in highly tactual cultures and environments. Ergo normal in childhood. May this not be the source of the abiding sense of reincarnation in non-literate societies and explain the lack of such sensation in literate societies? (Counterblast, 1969, 26)

oral culture is easily led to feel that something has been left out. Per­haps this is the origin of our feeling of déjà vu, the sense of having been “here” before. (Cliche to Archetype, 1970, 68)