Locke’s discussion, then, points up qualitative dimensions of durational experience that his explicit argument cannot account for. These qualitative dimensions arise from irregularities of succession and from intensities of sensations, aspects of “the succession of ideas” whose impact on our sense of duration Locke considers only indirectly. In Hume’s A Treatise of Human Nature (1738), however, these dimensions take center stage. Far more than Locke, Hume focuses on differentiating between “degrees and force of liveliness,” as Hume puts it throughout the first chapter of the Treatise. Hume distinguishes between impressions and ideas and devotes much attention to the passions, which he takes to deliver impressions of the strongest degree, in contrast to “the faint images of these in thinking and reasoning,” (1), which he calls ideas.”8 Hume also examines the logic of association among impressions and ideas much more thoroughly than Locke does. Whereas Locke posits succession as a singular principle requiring little analysis and devotes only one chapter to the association of ideas in which he primarily focuses on the dangers of chance connections, Hume argues that resemblance, contiguity, and cause and effect are all principles that universally and naturally encourage our relating one idea or impression to another thus complexly shaping thoughts and feelings (11).9 Hume proposes that such associative operations are responsible for both the diachronic movement of our minds—the succession of our ideas and impressions—and the synchronic resonances that reverberate in the mind at a single instant—the complex ideas and passions that yoke together a number of impressions and ideas into coherent notions of substance or mode.10 Furthermore, he distinguishes between the ways by which ideas connect to one another and the ways by which impressions do, arguing that “ideas are associated by resemblance, contiguity, and causation; and impressions only by resemblance” (283). For Hume, then, our minds are constituted to begin with by a variety of compositional principles, thus yielding varying qualities of association. Together these principles of association form “a kind of Attraction, which in the mental world will be found to have as extraordinary effects as in the natural, and to shew itself in as many and as various forms” (12–13).
Such privileging of sensible, affective, and compositional dimensions informs Hume’s discussion of time in Book I of the Treatise. Hume argues “that time cannot make its appearance to the mind, either alone, or attended with a steady unchangeable object, but is always discover’d by some perceivable succession of changeable objects” (35). But Hume directly recognizes that attention to such succession of perceptions yields notions not only of quantity, but also of quality. Hume defines “the idea of time” (34) as “an abstract idea, which comprehends a still greater variety than that of space, and yet is represented in the fancy by some particular individual idea of a determinate quantity and quality” (35). Qualities of duration arise because, according to Hume, our idea of time is “deriv’d from the succession of our perceptions of every kind, ideas as well as impressions, and impressions of reflection as well as of sensation” (34–35), thus including “internal impressions,” which he specifies as “our passions, emotions, desires and aversions” (33) and which he has earlier excluded from our idea of space. Moreover, Hume emphasizes that each and every one of the impressions and ideas that combine into our sense of time constitutes a substantial experience: “’Tis certain then, that time, as it exists, must be compos’d of indivisible moments” (31) that “must be fill’d with some real object or existence” (39), which he also calls “sensible qualities” (39). He does not count these “indivisible moments” as supporting our sense of time; following Locke’s explicit argument, only succession does this job for Hume. Yet he devotes much of his discussion to the experiential endurance of these units, highlighting their positivity. Hume defines the moment in Book I of the Treatise as, strictly speaking, not a part of time; and yet, he also attributes to it what Gilles Deleuze identifies in Hume’s philosophy as “real existence.” As Deleuze explains it, “real existence” is “neither a mathematical nor a physical point, but rather a sensible one,” and he adds, “a physical point is already extended and divisible; a mathematical point is nothing.” A sensible point is indivisible, and yet it is something.11
Beyond highlighting the moment as a part of endurance by virtue of its “sensible qualities,” Hume argues that our idea of time is not an object in and of itself, “but arises altogether from the manner, in which impressions appear to the mind” (36). A moment “must be fill’d with some real object or existence,” and our idea of time is created by the very principles of composition that string these real objects together. And if these principles of composition are by Locke’s analysis mere “succession,” then Hume’s analysis differentiates variable forms of succession. More specifically, Hume exemplifies succession as the order and rhythm in which musical notes appear, suggesting that even as principles of succession are not objects in and of themselves, they cannot be extricated from the existences through which they are perceived. Thus, Hume explains, “Five notes play’d on a flute give us the impression and idea of time; tho’ time be not a sixth impression, which presents itself to the hearing or any other of the senses…. But here it only takes notice of the manner, in which the different sounds make their appearance” (36–37). Such an explication of the succession that defines time produces it as an aesthetic form—both a logic of composition and an ineluctably experiential apprehension of it.
When Hume discusses measurement, he considers it to be more like an artist’s intuition inextricable from his practice than like a mathematical abstraction. In a long discussion of the unreliable precision of all our measures of size—of bodies and space as much of as of time—Hume comments about the aptness of our intuitive estimations of duration, analogizing these to artists’ intuitions about their media. He writes:
This appears very conspicuously with regard to time; where tho’ ’tis evident we have no exact method of determining the proportions of parts, not even so exact as in extension, yet the various corrections of our measures, and their different degrees of exactness, have given us an obscure and implicit notion of a perfect and entire equality. The case is the same in many other subjects. A musician finding his ear become every day more delicate, and correcting himself by reflection and