195. Hume begins with an account of the ‘perceptions of the human mind,’ which corresponds to Locke’s account of ideas with two main qualifications, both tending to complete that dependence of thought on something other than itself which Locke had asserted, but not consistently maintained. He distinguishes ‘perceptions’ (equivalent to Locke’s ideas) into ‘impressions’ and ‘ideas’ accordingly as they are originally produced in feeling or reproduced by memory and imagination, and he does not allow ‘ideas of reflection’ any place in the original ‘furniture of the mind.’ ‘An impression first strikes upon the senses, and makes us perceive heat or cold, thirst or hunger, pleasure or pain, of some kind or other. Of this impression there is a copy taken by the mind, which remains after the impression ceases; and this we call an idea. This idea of pleasure or pain, when it returns upon the soul, produces the new impressions of desire and aversion, hope and fear, which may properly be called impressions of reflection, because derived from it. These, again, are copied by the memory and imagination, and become ideas; which, perhaps, in their turn give rise to other impressions and ideas; so that the impressions are only antecedent to their correspondent ideas, but posterior to those of sensation and derived from them’ (Part I. §2). He is at the same time careful to explain that the causes from which the impressions of sensation arise are unknown (ibid.), and that by the term ‘impression’ he is not to be ‘understood to express the manner in which our lively perceptions are produced in the soul, but merely the perceptions themselves’. [1] The distinction between impression and idea he treats as equivalent to that between feeling and thinking, which, again, lies merely in the different degrees of ‘force and liveliness’ with which the perceptions, thus designated, severally ‘strike upon the mind.’ [2] Thus the rule which he emphasises [3] ‘that all our simple ideas in their first appearance are derived from simple impressions which are correspondent to them and which they exactly represent,’ strictly taken, means no more than that a feeling must be more lively before it becomes less so. As the reproduced perception, or ‘idea,’ differs in this respect from the original one, so, according to the greater or less degree of secondary liveliness which it possesses, is it called ‘idea of memory,’ or ‘idea of imagination.’ The only other distinction noticed is that, as might be expected, the comparative faintness of the ideas of imagination is accompanied by a possibility of their being reproduced in a different order from that in which the corresponding ideas were originally presented. Memory, on the contrary, ‘is in a manner tied down in this respect, without any power of variation’; [4] which must be understood to mean that, when the ideas are faint enough to allow of variation in the order of reproduction, they are not called ‘ideas of memory.’
[1] p. 312, note [Introduction to the Treatise of Human Nature]
[2] See pp. 327 and 375 [Book I, part I., sec. II. and part III. sec. II.]
[3] p. 310 [Introduction to the Treatise of Human Nature]
[4] p. 318 [Book I, part I., sec. III.]
‘Ideas’ that cannot be so represented must be explained as mere words.
196. All, then, that Hume could find in his mind, when after Locke’s example he ‘looked into it,’ were, according to his own statement, feelings with their copies, dividing themselves into two main orders—those of sensation and those of reflection, of which the latter, though results of the former, are not their copies. The question, then, that he had to deal with was, to what impressions he could reduce those conceptions of relation—of cause and effect, substance and attribute, and identity—which all knowledge involves. Failing the impressions of sensation he must try those of reflection, and failing both he must pronounce such conceptions to be no ‘ideas’ at all, but words misunderstood, and leave knowledge to take its chance. The vital nerve of his philosophy lies in his treatment of the ‘association of ideas’ as a sort of process of spontaneous generation, by which impressions of sensation issue in such impressions of reflection, in the shape of habitual propensities,’ [1] as will account, not indeed for there being—since there really are not—but for there seeming to be, those formal conceptions which Locke, to the embarrassment of his philosophy, had treated as at once real and creations of the mind.
[1] Pp. 460 and 496 [Book I, part III., sec. XIV. and part IV., sec. II.]
Hume, taken strictly, leaves no distinction between impressions of reflection and of sensation.
197. Such a method meets at the outset with the difficulty that the impressions of sensation and those of reflection, if Locke’s determination of the former by reference to an impressive matter is excluded, are each determined only by reference to the other. What is an impression of reflection? It is one that can only come after an impression of sensation. What is an impression of sensation? It is one that comes before any impression of reflection. An apparent determination, indeed, is gained by speaking of the original impressions as ‘conveyed to us by our senses;’ but this really means determination by reference to the organs of our body as affected by outward bodies—in short, by a physical theory. But of the two essential terms of this theory, ‘our own body,’ and ‘outward body,’ neither, according to Hume, expresses anything present to the original consciousness. ‘Properly speaking, it is not our body we perceive when we regard our limbs and members, but certain impressions which enter by the senses.’ Nor do any of our impressions ‘inform us of distance and outness (so to speak) immediately, and without a certain reasoning and experience’. [1] In such admissions Hume is as much a Berkeleian as Berkeley himself, and they effectually exclude any reference to body from those original impressions, by reference to which all other modes of consciousness are to be explained.