‘Genealogy is gray, meticulous and patiently documentary.’ The opening statement of Michel Foucault's 1971 essay ‘Nietzsche, Genealogy, History’ reiterates Friedrich Nietzsche's polemics against ‘the genuinely English type’ of genealogy, ‘gazing around haphazardly in the blue’, launched in the preface to On the Genealogy of Morals. As the antidote to the ethereal realms of the soul and sky hypothesised in earlier genealogies of humankind's development, the German philosopher advances his own grey tactics, determined to mine ‘the entire long hieroglyphic record, so hard to decipher’.

Turning away from human interiority and the perceived grand teleologies of Spirit and Reason, grey genealogy traverses the exterior margins of a vast and often discouraging terrain overlain with opacities, densities and minutiae, not in order to retrieve some transcendental signifier hidden beneath or beyond the ‘field of entangled and confused parchments’, but to demonstrate how the very idea of origins, essences and first principles has been retroactively constructed and subsequently covered over. As a general strategy, Foucault delineates his concepts negatively by cropping out what they are not. Discourse, he asserts, is not, ‘a manifest, visible, coloured chain of words’. Consequently the genealogist should ‘not pretend to go back in time to restore an unbroken continuity’. In the two programmatic declarations made a century apart by Nietzsche and Foucault, greyness denotes the dense and disjunct strata uncovered in the genealogical analysis of descent, or what the opening sentence of The Archaeology of Knowledge describes as, ‘the movements of accumulation and slow saturation, the great silent, motionless bases that traditional history has covered with a thick layer of events’.

The thesis that knowledge and reason are historically contingent, obeying the provisional and unconscious roots of a period's dominant episteme, was first formulated in The Order of Things: An Archaeology of the Human Sciences. Working at the fringes of discursive formations, the archaeological method crafted by Foucault is not concerned with language as an instrument to express emotions or communicate ideas, nor with the content or message of individual texts, but as a framework that regulates the conditions of possibility of what can be said or thought at a given time. In the renowned analysis of Diego Velázquez's painting Las Meninas (1656) undertaken in the opening pages of the book, the author reflects on the limits of his own ekphrasis by appealing to a tenacious greyness.