Most of my readers will have observed a small water-insect on the surface of rivulets, which throws a cinque-spotted shadow fringed with prismatic colours on the sunny bottom of the brook; and will have noticed, how the little animal wins its way up against the stream, by alternate pulses of active and passive motion, now resisting the current, and now yielding to it in order to gather strength and a momentary fulcrum for a further propulsion. This is no unapt emblem of the mind’s self-experience in the act of thinking. There are evidently two powers at work, which relatively to each other are active and passive; and this is not possible without an intermediate faculty, which is at once both active and passive. In philosophical language, we must denominate this intermediate faculty in all its degrees and determinations, the IMAGINATION.
This idea represented Coleridge’s attempt to move beyond conflictual thinking — what his friend John Thelwall called his “theory of Collision of Ideas” — toward something more dialectical — “mutual Propulsions” (Collected Letters 1, 636).
Peristalsis is the sequential rhythmic contraction or undulation of muscles (Gk peri-, stellein “contracting around“), especially in the bowel (which we know was a problem for Coleridge due to his intake of constipatory opiates). It is instructive to think how the movement of his bowels might have influenced his thinking (the nexus is there in our idea of digestion as nutritive or cognitive, as psychosomaticists — like Freud and Fliess — and those who suffer food allergies know).
(Re the image of the “cinque-spotted shadow”: Coleridge loves fives, hence his holistic “quinquarticular Dialectic” or “logo-noetic Pentad” — namely prothesis, thesis, antithesis, mesothesis ["the Indifference"] and synthesis, or two polarities and their “co-involution” — exemplified in his “Pentad of Operative Christianity” [Christ the Word, Scripture, Church, Holy Spirit and Preacher] from Confessions of an Enquiring Spirit, but also in the Powers of Nature [attraction, repulsion, contraction, dilation and centrality], the Colours [red, yellow, blue, orange/violet, green] and the races. His prime emblem is the “compass of nature.”)
Ephemeroptera (mayfly; from ephemeron, “lasting only a day” + pteron “wing”)
See also chapter 7 of the Biographia, where he uses a similar analogy, that of a kind of reculer pour mieux sauter (lit. withdraw to better leap), to describe how writers can best connect with their readers:
The reader should be carried forward, not merely, or chiefly, by the mechanical impulse of curiosity, or by a restless desire to arrive at the final solution; but by the pleasurable activity of mind, excited by the attractions of the journey itself. Like the motion of a serpent, which the Egyptians made the emblem of intellectual power; or like the path of sound through the air; at every step he pauses, and half recedes, and, from the retrogressive movement, collects the force which again carries him onward.
(MEM echoes this passage from Coleridge at “DRAGONS, DIGESTION, KNOWLEDGE FARMS: Peristalsis” [Faces of Sound 18 Apr. 2009].)
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S[amuel] T[aylor] Coleridge, Biographia Literaria: or, Biographical Sketches of MY LITERARY Life and OPINIONS (New York: Leavitt, Lord and Co., 1834).
For Coleridge’s meta-science, see Trevor Hartley Levere, Poetry Realized in Nature: Samuel Taylor Coleridge and Early Nineteenth-Century Science (Cambridge, England: CUP, 1981) [esp. 114-20].