"This requirement that nature should be continuous does not take exactly the same form in the systems as it does in the methods. For the systematician, continuity consists only of the unbroken juxtaposition of the different regions that can be clearly distinguished by means of characters; all that is required is an uninterrupted gradation of the values that the structure selected as a character can assume in the species as a whole; starting from this principle, it will become apparent that all these values are occupied by real beings, even though they may not yet be known. 'The system indicates the plants, even those it has not mentioned; which is something that the enumeration of a catalogue can never do' (Linnaeus, Philosophie botanique, section 156). And the categories will not simply be arbitrary conventions laid out over this continuity of juxtaposition; they will correspond (if they have been properly established) to areas that have a distinct existence on this uninterrupted surface of nature; they will be areas that are larger than individuals but just as real. In this way, according to Linnaeus, the reproductive system made it possible to establish the existence of indisputably well-founded genera: 'Know that it is not the character that constitutes the genus, but the genus that constitutes the character, that the character derives from the genus, not the genus from the character' (Ibid., section 169). In the methods, on the other hand, since resemblances — in their massive and clearly evident form - are posited to start with, the continuity of nature will not be this purely negative postulate (no blank spaces between distinct categories), but a positive requirement: all nature forms one great fabric in. which beings resemble one another from one to the next, in which adjacent individuals are infinitely similar to each other; so that any dividing-line that indicates, not the minute difference of the individual, but broader categories, is always unreal. There is a continuity produced by fusion in which all generality is nominal. Our general ideas, says Button, are relative to a continuous scale of objects of which we can clearly perceive only the middle rungs and whose extremities increasingly flee from and escape our considerations . . . The more we increase the number of divisions in the productions of nature, the closer we shall approach to the true, since nothing real ly exists in nature except individuals, and since genera, orders, and classes exist only in our imagination (Buffon, Discours sur la manière de traiter l'histoire naturelle (Œuvres complètes, t. I, pp. 36 and 39).Bonnet, meaning much the same thing, said:There are no leaps in nature: everything in it is graduated, shaded. if there were an empty space between any two beings, what reason would there be for proceed ing from the one to the other? There is thus no being above and below which there are not other beings that are united to it by some characters and separated from it by others.It is therefore always possible to discover 'intermediate productions', such as the polyp between the animal and the vegetable, the flying squirrel between the bird and the quadruped, the monkey between, the quadruped and man. Consequently, our divisions into species and classes 'are purely nominal'; they represent no more than 'means relative to our needs and to the limitations of our knowledge, (Charles Bonnet, Contemplation de la nature, lère partie (Œuvres complètes, t. IV, pp. 35-6))."
(Foucault, 2003, p.159-160)
Foucault, M. (2003). The Order Of Things. London, Routledge.
"To be able to exist as a science, natural history must, then, presuppose two groupings. One of them is constituted by the continuous network of beings; this continuity may take various spatial forms; Charles Bonnet thinks of it sometimes as a great linear scale of which one extremity is very simple, the other very complicated, with a narrow intermediary region - the only one that is visible to us - in the centre; sometimes as a central trunk from which there is a branch forking out on one side (that of the shellfish, with the crabs and cray-fish as supplementary ramifications) and the series of insects on the other, branching out to include the frogs (C. Bonnet, Contemplation de la nature, chap. XX, pp. 130-8); Buffon defines this same continuity 'as a wide woven strip, or rather a bundle which every so often puts out side branches that join it up with the bundles of another order' (Buffon, Histoire naturelle des oiseaux - 1770, t. I, p. 396); Pallas sees it as a polyhedric figure (Pallas, Elenchus Zoophytorum- 1786); Hermann wished to constitute a three-dimensional model composed of threads all Starting from a common point of origin, separating from one another, 'spreading out through a very great number of lateral branches', then coming together again (J. Hermann, Tabulae affinitatum animalium - Strasbourg, 1783, p. 24). The series of events, however, is quite distinct from these spatial configurations, each of which describes the taxonomic continuity in its own way; the series of events is discontinuous, and. different in each of its episodes; but, as a whole, it can be drawn only as a simple line, which is that of time itself (and which can be conceived as straight, broken, or circular). In its concrete form, and in the depth that is proper to it, nature resides wholly between the fabric of the taxinomia and the line of revolutions. The tabulations that it forms in the eyes of men, and that it is the task of the iscourse of science to traverse, are the fragments of the great surface of living species that are apparent according to the way it has been patterned, burst open. and frozen, between two temporal revolutions."
(Michel Foucault, The Order Of Things p. 163)
Foucault, M. (2003). The Order Of Things. London, Routledge