My interest in Kant made it imperative for me to turn to Locke, to whom Kant often refers in his Critique of Pure Reason as ‘the famous Locke’ (der berühmte Locke); Locke’s derivation of all our ideas from two empirical sources, sensation (‘employed about external sensible objects’) and reflection (‘employed about the internal operations of our minds’, An Essay Concerning Human Understanding, Bk. II, Ch. 1, par. 2), stands in sharp contrast to Kant’s insistence that the ‘intuitions’ (Anchauungen) of space and time are a priori conditions of all empirical sensations and reflections (see ‘The Kantian subjectivity of space and time’ on my blog, posted on June 14). And so I came to Locke’s notion of duration, which appears to critically point back to Aristotle’s derivation of time from phora, i.e. locomotion, and to positively point towards Kant’s purely subjective ‘intuition’ (Anchauung) of time (see ‘Aristotle’s concept and Kant’s ‘intuition’ of time’ on my blog, posted on July 29).
Aristotle’s discussion of time in the Physics comes after the discussion of place, and Locke’s discussion of duration follows his discussion of space. This arrangement is not accidental. Aristotle defines time as the number of motion of a body moving in place/space (topos), Locke views space as an idea derived from a distance between bodies perceived by sight or by touch, and time as a simple mode of duration, which ‘is another sort of distance, or length, the idea whereof we get not from the permanent parts of space, but from fleeting and perpetually perishing parts of succession.’ (Essay, Bk. II. Ch. XIV, par. 1).
Locke explains: ‘It is evident, to anyone who will but observe what passes in his own mind, that there is a train of ideas which constantly succeed one another in his understanding, as long as he is awake. Reflection on these appearances of several ideas one after another in our minds is that which furnishes us with the idea of succession; and the distance between any parts of that succession, or between the appearance of any two ideas in our minds, is that we call duration.’ (Ch. XIV, par. 3)
Locke insists that we derive the idea of duration from reflection, which is ‘employed about the internal operations of our minds’, not from sensation, which is ‘employed about external sensible objects’: ‘It is to me very clear that men derive their ideas of duration from their reflection on the train of the ideas they observe to succeed one another in their own understandings’ (par. 4). ‘Thus by reflecting on the appearing of various ideas one after another in our understandings, we get the notion of succession; which if anyone should think we did rather get from our observation of motion by our senses, he will perhaps be of my mind when he considers that even motion produces in his mind an idea of succession no otherwise than as it produces there a continued train of distinguishable ideas’ (par. 6).