Hume's Relative Ideas

55. HUME'S RELATIVE IDEAS The fundamental principle in the analysis of propositions containing descriptions is this: Every proposition which we can understand must be composed wholly of constituents with which we are acquainted. Bertrand Russell, The Problems of Philosophy In this paper I shall show that Hume found within the "way of ideas" the basis for a distinction between knowledge by acquaintance and knowledge by description. By examining the distinction between positive and relative ideas and Hume's discussions of relative ideas in the light of the logical writings of Antoine Arnauld and Isaac Watts, I shall argue that relative ideas are the cognitive analogues of definite descriptions. Although Hume often regarded epistemic claims based upon relative ideas with at least a modicum of scepticism, the doctrine of relative ideas provides the basis for the intelligibility of and the critical moves in his discussions of that unintelligible chimera of... substance. The recognition that Hume espoused the doctrine of relative ideas also sheds light on his discussions of the missing shade of blue and his claim that one has an idea of the thousandth part of a grain of sand, even though one's mental image of that minute entity differs in no way from one's mental image of an entire grain of sand. I. Positive and Relative Ideas Empiricism was the predominant intellectual force in early eighteenth century British philosophy. It was on the basis of their commitment to empiricism that such philosophers as Locke and Berkeley granted ontological status to those qualities that are directly available to the senses. As states of mind, ideas were held either to represent real qualities and objects (Locke) or to be real qualities and 56. objects (Berkeley). Nonetheless, as substance theorists, the ontological commitments of both Locke and Berkeley went beyond the domain of a pure ontology of qualities, and since substance is in principle imperceptible, such an ontological commitment seems to raise a problem for an empirical theory of ideas. Although it might be reasonable to assume that an idea of a quality is a mental image of that quality, such a claim is less plausible regarding one's ideas of substance. The early empiricists responded to this apparent problem by drawing a distinction between two kinds of ideas: positive ideas and relative ideas. A positive idea represents an entity as it is in itself, and it might be reasonable to construe such ideas as mental images. On the other hand, a relative idea—what Berkeley often called a notion 4 or a relative notion —singles out an unperceived entity on the basis of its relations to a perceived entity, i.e. , a positive idea. Both Locke and Berkeley were explicit in claiming that one has no positive idea of substance. For example, Locke wrote: We have no such clear Idea at all, and therefore signify nothing by the word Substance , but only an uncertain supposition of we know not what; (i.e. of something whereof we have no particular distinct positive) Idea, which we take to be the substratum, or support of those Ideas we do know. On· has only an "obscure and relative Idea of Substance in general", indeed, "we have no Idea of what it [substance] is, but only a confused and obscure one of what it does." O» this point Berkeley was at one with Locke. Regarding one's putative ideas of material substance, he wrote the following: Now I desire that you would explain what is meant by matter's supporting extension: say you, I have no idea of matter, and therefore 57. cannot explain it. I answer, though you have no positive yet if you have any meaning at all, you must have at least a relative idea of matter; though you know not what it is, yet you must be supposed to know what relation it bears to accidents , g and what is meant by its supporting them. Notice that in the writings of both Locke and Berkeley one's idea of substance is not a positive idea: one has no idea that represents substance as it is in itself. The most one can claim to have is a relative idea of substance...