Hume, David (1711–76)

DOI: 10.4324/9780415249126-DB040-2
Version: v2,  Published online: 2005
Retrieved January 16, 2019, from

7. The external world

The newly mechanistic natural science of the seventeenth and eighteenth centuries sharpened the question of what and how one can know of the external world through sensation. One of Hume’s aims in the Treatise is to investigate ‘what causes induce us to believe in the existence of body’ (THN 1.4.2), although he remarks at the outset of the investigation that ‘it is in vain to ask, Whether there be body or not? That is a point which we must take for granted in all our reasonings’. He analyses the belief in ‘bodies’ (physical objects) as the belief in objects that have a ‘continu’d and distinct’ existence: that is, in objects that continue to exist when not perceived by the mind and that have an existence that is distinct from the mind in virtue of existing outside of it and in causal independence of it with respect to their existence and operations. The ‘vulgar’ – which includes even philosophers, for most of their lives – attribute a continued and distinct existence to some of what they immediately perceive, even though what they immediately perceive are in fact impressions. The opinion that these impressions have a continued and distinct existence cannot itself be an immediate product of the senses, Hume argues, for the senses themselves cannot perceive the continuation when unperceived, or even the distinct existence of what they perceive immediately; nor can the opinion be a proper subject of inference, since reasoning shows instead that what we immediately perceive are not continued and distinct existences, but dependent and perishing impressions in the mind. The opinion in question must, therefore, depend on features of the imagination (in the narrow sense).

How then does the belief in bodies arise? As Hume explains it, some of our impressions (for example, those of colour, sound, taste, smell and touch) exhibit constancy and coherence. Constancy is their tendency to return despite interruptions; coherence is their tendency to occur in a certain order and to manifest elements of that order at similar times even through interruption. The coherence of impressions plays a role in the tendency to attribute continued and distinct existence to those impressions, since by means of the supposition of such existence the mind can attribute greater causal regularity to them than would otherwise be possible – and once the mind becomes accustomed to looking for causal regularities, it carries this tendency on even beyond what it originally finds in experience. The primary cause of the attribution of continued and distinct existence to what are in fact impressions, however, is their constancy, Hume maintains. The mind easily confuses a ‘perfectly identical’ – that is, invariable and uninterrupted – object with a sequence of resembling but interrupted ones, because the feeling to the mind is itself similar in the two cases. Accordingly, the mind attributes a perfect identity to some of its interrupted impressions. At times when the mind becomes aware of the interruption, it seeks to reconcile the contradiction by supposing that the very impressions themselves continue to exist uninterruptedly, distinct from the mind, during the moments when they are not perceived. The force and vivacity of the impressions provides the liveliness required for this supposition to constitute a belief.

The vulgar opinion that the very things we immediately perceive have a continued and distinct existence apart from the mind is not, Hume argues, contradictory or inconceivable; but it can, none the less, easily be shown to be false by a few simple experiments. Pressing one’s eyeball, for example, doubles one’s visual impressions, thereby showing that they are not causally independent of the mind for their existence or operation, and from this it can be inferred that they do not continue to exist when not perceived. Yet the opinion that there are continued and distinct existences is, Hume asserts, psychologically so irresistible that, far from giving it up, philosophers invent a new theory to reconcile their experiments with it. This is the philosophical theory of ‘double existence’, according to which sensory impressions are caused by a second set of objects – bodies – that resemble them qualitatively. This theory, Hume argues, has no primary recommendation to the imagination – for the imagination naturally gives rise instead to the original vulgar view that our impressions themselves are continued and distinct. Nor does the theory have any primary recommendation to reason – for causal reasoning can conclude that an object of a given kind exists only if it has been observed to be constantly conjoined with an object of another kind, yet on the philosophical theory, we directly observe only impressions, not bodies accompanying impressions. When he considers intensely the causal origin of the belief in bodies, Hume reports that he loses confidence in the belief, his earlier claim that we must take it for granted notwithstanding. However, this state of doubt is only temporary, for belief in bodies (in one form or other) immediately returns as soon as one’s attention is turned away from the question.

A further problem concerning the content of the belief in bodies arises from what Hume calls ‘the modern philosophy’ (THN 1.4.4). It is a central contention of the modern philosophy that such qualities as extension, solidity and motion really exist in bodies, but that qualities resembling our impressions of colours, sounds, tastes, smells and tactile qualities (such as heat and cold) do not really exist in bodies. This is, for example, Locke’s claim concerning what he calls ‘primary’ and ‘secondary’ qualities (see PRIMARY–SECONDARY DISTINCTION). Hume judges that there is, among the various arguments of the modern philosophers for this conclusion, one that is ‘satisfactory’. It is found that the perception of colour, sound, taste, smell, heat and cold varies with different perspectives and different states of one’s body; and hence it follows that bodies cannot have all of the qualities of colour, sound, taste, smell, heat or cold that they are perceived to have. Hence, he argues, from the principle (which is one of his ‘rules by which to judge of causes and effect’) that ‘like effects have like causes’, we may conclude that none of these qualities exist in bodies themselves. Yet the qualities of extension, solidity and motion of bodies cannot be conceived without conceiving colours or tactile qualities to fill the extension of the body in which they supposedly occur; hence, it follows that bodies cannot be determinately conceived at all in strict accordance with the modern philosophy. Since this ‘satisfactory’ argument is a causal one, Hume presents the outcome as a conflict between causal reasoning and ‘our senses’ – meaning by the latter term, more specifically, the operations of the imagination on impressions of sensation that give rise to the belief in bodies.

Citing this article:
Garrett, Don. The external world. Hume, David (1711–76), 2005, doi:10.4324/9780415249126-DB040-2. Routledge Encyclopedia of Philosophy, Taylor and Francis,
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