In his first Critique, Immanuel Kant orients reason in relation to the planetary surface, and thus to human bipedalism. He writes that, although the earth appears to one’s immediate senses as a flat surface extending indefinitely to the horizon, we can nevertheless, ‘in accordance with a priori principles’, know that it is a ‘sphere’ with ‘diameter’, ‘magnitude’ and ‘limits’. Clearly intending a comparison between the two, the philosopher then adds that ‘our reason’ is, in identical fashion, ‘not like an indeterminably extended plane’ but ‘must rather be compared to a sphere’.
This comparison, between the space of reasons and that of our globe, serves to dramatize Kant’s master-idea of the togetherness of empirical receptivity and conceptual articulation: the conviction that, although the cascading content of sensation is unbounded or infinite (in the same sense as, in traversing a sphere’s continuous surface, we discover no boundary or edge), the conceptual functions and maxims of reason governing this experience afford to is structuring ‘limits’ (just as, embedded within three dimensions, the sphere is indeed spatially infinite). Crucially, it is these bounds alone that make knowledge possible, in that they anatomize our judgings into those that are correct and those that are incorrect; with then in place, we no longer simply perceive objects in a prehensive sense – our perceptions gain a standard of objectivity against which they can be continually appraised and upbraided (thus contending, in our unfolding engagements with the world, for the epithet ‘objective’).
According to the critical philosophy, such limits are to be interpreted exclusively in juridical terms: they concern the irrealis scope of ‘ought’ rather than the realis scope of ‘is. Yet in selecting this particular tellurian image, Kant unwittingly reminds us that we do not ‘orient’ ourselves in thinking through a judicial ‘ground of differentiation’ alone. For we are able to orient ourselves upon Earth’s mundane sphere only because of the contingent fact of our vertical posture, our orthograde backbone. Reason’s supererogations rest upon our standing so. And this introduces a whole new plot thread, a cord upon which genealogy can pull.
In his Physical Geography, having once again compared the rational ‘whole’, Kant suggests that each person may triangulate their location within spheriform terrestrial space, and thus unequivocally orient themselves, by drawing a line upward from their head into the heavens, and downward through their pelvis into the earth. One’s latitude may then be ascertained by measuring the angle between this extended spinal axis and the earth’s axis of rotation.
It is only because, uniquely among vertebrates, the human spine’s axis traces a continuation of Earth’s own radius, that we can extrapolate its trajectory ad coelum et ad inferos – upwards towards a supernal zenith and downwards to a hypogene nadir. Drawing an imaginary great circle whose diameter connects the points of this imagined zenith and it’s caudal nadir as antipodes, the observer can become aware of themself as the centre point of a so-called celestial meridian. From here, they can locate themselves upon the planet by measuring the angle between the celestial pole (the point around which the stars appear to rotate) and the zenith of their vertebral axis (the point at which the extended line of the spire pierces outer space). This allows one to compute one’s latitude, or, as Kant puts it, ‘the distance from the equator’, and thus to acquire one’s North-South coordinates.
It would therefore seem that a quirk of spinal morphology is responsible for placing humans in direct relation with the figure of the earth, fomenting the human propensity for geo-desic abstraction in a fashion entirely barred to pronograde quadrupeds–those flatlanding crustcrawlers who experience the planet only as a surface indefinitely far extended. Triggering the carving up of the planet with reticulating graticules and navigational rhumb lines, sapience’s conquering of global space proceeds from and rests upon a lumbar foundation whose verticality sets our species apart, instigation a ratio-technical line of development extending from the first anthropoid’s binocular gaze upon its forelimb workspace all the way to geostationary satellite above. What Kant’s spinal thought-experiment hints at, then, is that Homosapiens’ ability to exert cognizance and control on a planetary scale results from the same species-specific peculiarity as it’s susceptibility to back pain.