In Science and the Modern World (SMW below) Whitehead cites Francis Bacon from his posthumous Silva Silvarum (ca 1625):

It is certain that all bodies whatsoever, though they have no sense, yet they have perception: for when one body is applied to another, there is a kind of election to embrace that which is agreeable, and to exclude or expel that which is ingrate; and whether the body be alterant or altered, evermore a perception precedeth operation; for else all bodies would be alike one to another. (52)

Whitehead comments repeatedly on this passage in SMW:¹

[in the Silva Silvarum passage] note the careful way in which Bacon discriminates between perception, or taking account of, on the one hand, and sense, or cognitive experience, on the other hand. (52)

The word ‘perceive’ [along with ‘percept’ and ‘perception’] is, in our common usage, shot through and through with the notion of cognitive apprehension. So is the word ‘apprehension’ even with the adjective ‘cognitive’ omitted. [Therefore, instead of ‘perceive’/’percept’/’perception’,] I will use the word ‘prehension’ for uncognitive apprehension (86)

Bacon’s words, “all objects would be alike one to another” (…) really means that (…) what each (…) object is in itself becomes relevant to the one limited value emergent in the guise of the event.² (130)

The great point made by Bacon, and by Whitehead in turn, is that all things have inherent form “for else all bodies would be alike one to another” such that the ‘world’ would be an undistinguished and undistinguishable uniformity. Instead, the world fits together through universal differentiation that is inherent (but not, of course, necessarily known). And it is this inherent differentiation in form from the smallest particles to whole galaxies which is at work, or which expresses itself, in their interaction — and everything is in differentiated interaction.

What characterizes the particularity (“limited value” in the mathematical sense) of any and all events whatsoever is the interaction of inherent forms. They exist, as Whitehead has it, by “taking account” of one another and only in this way. 

Leibniz put the same point a century after Bacon in his stipulation that each and every thing — as a distinguished/distinguishing monad — is a mirror of the universe since its inherent form takes part in the complete complex of all the events that are. Each monad therefore informs both about itself and about the surrounding universe into which it must fit in its own particular way in order to exist at all.

Bacon and Whitehead — and McLuhan in his turn — call this inherent form in all things “perception” (though not without notable inconsistently, ie, not without sometimes themselves using it to imply or even outright mean ‘conscious apprehension’).³

This facility is not “cognitive” by nature, but humans are never without at least a vague self-consciousness that there is something variable ‘behind’ experience, like moods. And because humans have an inherent ability to grasp the general being of things, possibly including the being of perception (dual genitive) as this variable ‘behind’ experience, it might become “cognitive” in the same way as geometric forms and chemical elements and biological genes have become cognitive.

Of course such cognition is always “limited” in a great number of ways (only hence, the truly wondrous progress of science), but the initiation of cognitive awareness in any area is always noteworthy and some initiative events are so consequential that history is never the same again. This is true of the infant’s history after it learns to speak and it is just as true of history at large after such seminal events as the species beginning to speak — or its learning to represent speech in letters — or its learning to print letters mechanically — or its learning to print (and do everything else) with electricity — or its learning the general application of electric digitality in cybernetics (and, according to McLuhan in all literature via the epyllion structure) — or its learning (perhaps! — this is the great question posed by McLuhan) how such digitality⁴ might in turn illuminate even perception itself and so initiate a whole series of new sciences of the human “interior landscape”.⁵

In 1958, the same year as McLuhan began admonishing that “the medium is the message”, he also began insisting that media give “light through [towards us] not light on [from us]”. That is, media first of all in-form our cognition and experience generally — like light coming through a stained glass window — and have done so in some fashion ‘always already’. In this metaphor, the colors and shapes of the stained glass window may be taken to represent the existing form of perception — subjective genitive! — that human beings can never be without and that is therefore necessarily already in place when the light of some medium comes through it toward us.⁶

Media illuminate us,⁷ not we them. Hence, they are not in the first instance conceptual stances taken up by us to understand external or even internal matters. They are prior to this. They are perceptual forms (Bacon) or prehensive forms (Whitehead), not cognitive forms!

For McLuhan, similarly, media are perceptual forms, plural, and his admonition that “the medium is the message” would have us perceive media in their plurality as such perceptual forms. The circularity here, like the plurality, is essential: media are perceptual forms that must be perceived in order to be known. The question is only whether this kaleidoscope can be turned in such a way that these forms become subject to cognitive investigation.