In July 1978, as part of Louis Forsdale’s course on communication at Columbia¹, McLuhan and Forsdale conducted a dialogue of sorts (with McLuhan doing nearly all the talking, of course). McLuhan’s remarks on phenomenology are particularly worthy of note:

I mentioned this peeping through — the light coming through the situation — that is called (…) ‘phenomenology’. It took me a long time to discover [this correlation with my own work], the phenomenologists manage to cover their tracks pretty well. They like to make out that they are very serious bunch, hard-headed logical people, the Heideggers and the Husserls and so on. All they’re telling you — and this has been so ever since Hegel and his phenomenological stuff — ever since Hegel, all they’ve been telling you is that behind every situation there’s another situation that peeps through. That peeping through is phenomenology. I call it simply the medium is the message or the figure and the ground. The ground comes through the figure or the figure comes through the ground, it can be both ways. It’s that process of light through that is phenomenology. (…)² My Understanding Media is phenomenology of the media. (74:55-76:55) 

I have a book sort of ready to appear and I think I’ll now call it the Phenomenology of the Media — but it’s called Laws of the Media at the present time (87:54-88:05)

McLuhan says that “behind every situation there’s another situation that peeps through and that peeping through is phenomenology.” Hence, the complex relation or ratio of a figured “situation” to its grounding “situation” is constant. The fact of this relation does not result from diachronic development, but is something that is always the case. Just as in chemistry where elements always ‘peep through’ all physical materials, expressing themselves in them, so, according to McLuhan, in every psychological or spiritual event its ground is always “peeping through” — and it was the aim of the new science he wanted to found to learn how to read this:

To provide ways of discerning these lines of force, these currents not of opinion but of perception, is the aim of the Project in Understanding New Media³

At the same time, this constant (or synchronic) relation of figure to ground and of ground to figure is never the same. It is subject to a myriad variations over time. Hence, time is no singular. It is both synchronic and diachronic at once, so that it, too, appears only in a variable figure/ground co-relation: 

time considered as sequential (left hemisphere) is figure and time considered as simultaneous (right hemisphere) is ground. (Global Village, 10)

The claim is that neither figure nor ground can be understood unless each of them is seen in its essential relation to the other. This essential relation of mutual expression is the medium that is the message (of their “mutual expression”): 

I call it simply the medium is the message or the figure and the ground. The ground comes through the figure or the figure comes through the ground, it can be both ways. (75:48-76:02)

Together these complex points define where consideration of McLuhan’s work must begin: the fundamental plurality of time and the essential relation between figure and ground. It itself is able to be the investigation of figures in their grounds only as a figure itself, one that comes through its own grounding in these interrelated points.