We cannot transcend our “flat earth” view of media so long as we rely on private impressions at a particular time and place. The meaning and effect of a medium is the sum total of all its impact upon psyche and society. (McLuhan to Harry Skornia, July 6, 1964, Letters 305)

In chemistry, the sum total of the impact of any reaction on the physical world is — chemistry!

Impact radiates out from a physical reaction¹ in an endless series of waves like a stone dropped in a pond. But it is useless to try to trace those endless repercussions, since the overwhelming majority of them are inconsequential. Besides, they are indeed endless and an account of them, too, could never end.² Instead, we are able to repose in the knowledge that all of the endless impacts of any reaction are covered by the field of chemistry — and if any one of them turns out to be consequential, it may be illuminated in turn within that field. (Occasionally, of course, some peculiar reaction forces us to revise our notion of the field in what amounts to a ‘scientific revolution’. But this, too, belongs to chemistry and, far from undermining it, is one of its great motors. Or, findings in a field may lead to the founding of a new field like organic chemistry from chemistry. But this, too, is simply the way science works and amounts to no disruption of it. On the contrary!)

McLuhan had a comparable notion of media. His idea was that media have an endless impact on individuals and societies, but our study of those impacts need not be exhaustive. Indeed, it cannot be exhaustive!³ Instead a field must be established within which any impact can be studied in a limited way and which would be illuminating only because so limited! The main thing was simply to start and then to allow the normal workings of science to deal with problems, imprecisions, contradictions, and unknowns — etc etc.⁴ Hence — a signpost indicating an impending advance in understanding — “You mean my whole fallacy is wrong?”