I’m vaguely considering making this a series and explaining each section of Hume’s Treatise with one diagram. I think 5-6 of you would really appreciate that and several hundred of you would really not.
The first section of the Treatise is both short and pretty straightforward, but it goes a long way towards illustrating the affinity Deleuze always saw in Hume with Bergson and Spinoza. Like both of those latter thinkers, Hume is an absolutely practical thinker who begins with what D&G call a “conceptual plane of immanence.” Where thinkers like Descartes and Hegel begin with a single fundamental opposition with an excluded middle (such as certainty and doubt for Descartes, or Self-Consciousness and non-being for Hegel) and construct their ontology on the basis of this first opposition, Hume begins instead not with a thing or a rule but with a set of conceptual coordinates. We have not two opposing concepts or even two pairs of opposing concepts, but rather two spectra which delineate between them a range of possible objects: the graph shape of the above diagram is not accidental.
The place (and hence nature) of any given object in the plane of consistency depends on its position relative to both spectra. In other words, it’s not that a given perception is either an idea or an impression, and then, if an idea, either a simple or a complex idea. (This is the difference between a plane of consistency and a typology or schema). Rather, the proximity and distance from all four of these qualifiers (idea, impression, simple, complex) determines the nature of the object under consideration. In this we discover Hume’s affinity with Bergson’s method, especially as presented in Matter & Memory: As in Bergson, differences in degree along a spectrum become differences in kind by a process of increasing differentiation: thus ideas and impressions are two distinct phenomena, even though, as Hume says, “the difference betwixt these consists in the degrees of force and liveliness.” As Hume says later in the Treatise, “Where-ever the imagination perceives a difference among ideas, it can easily produce a separation.”