Hume's Science of Human Nature

Scientific Realism, Reason, and Substantial Explanation

David Landy

• Publisher: Routledge
• Year: 2017
• ISBN:
  9781351383240
• Edition: 1
• Topic: Philosophie
• Subtopic: Histoire et théorie de la philosophie

Hume's Science of Human Nature is an investigation of the philosophical commitments underlying Hume's methodology in pursuing what he calls 'the science of human nature'. It argues that Hume understands scientific explanation as aiming at explaining the inductively-established universal regularities discovered in experience via an appeal to the nature of the substance underlying manifest phenomena. For years, scholars have taken Hume to employ a deliberately shallow and demonstrably untenable notion of scientific explanation. By contrast, Hume's Science of Human Nature sets out to update our understanding of Hume's methodology by using a more sophisticated picture of science as a model.

1
Two Case Studies

The Impression-Idea and Simple-Complex Distinctions

The strongest part of the case for understanding Hume’s conception of the science of human nature as proceeding along the robustly realist lines that I will argue it does comes from a careful examination of his actual procedure in conducting that science. That is, while I will present evidence in the following chapters that Hume’s explicit statements about science can be read as expressing his commitment to realism, that the case for reading Hume as an inductivist about scientific methodology is insufficient, and that all of his most important conclusions are reached via arguments that proceed using the methodology that I ascribe to him, the hard core of my interpretation consists of exposing the underlying logical structure of Hume’s methodology in conducting his own investigation into the nature, powers, and essence of the human mind.

What I will argue in this chapter is that despite Hume’s apparent commitment to a very strong form of nominalism about qualities and relations, his own pursuit of the science of human nature commits him to the reality of the qualities of and relations between the various kinds of perceptions that he takes to constitute the human mind. Specifically, I will show that both the impression-idea distinction and the simple-complex distinction are best understood as theoretical hypotheses about the real differences that underlie and explain the observed regularities of human thought.

My procedure here will be as follows. I will begin by briefly outlining Hume’s theory of mental representation with an emphasis on the role of the Copy Principle in that theory and the surprising use to which it is put in general representation. Much of this material will likely be familiar, but its central importance to Hume’s project, as well as a recent renewal of interest in the topic by Hume scholars, warrants review. I will then present a puzzle about the role of his theory of general representation in Hume’s pursuit of the science of human nature, and specifically its compatibility with two of Hume’s most important theoretical-explanatory moments: his drawing of the impression-idea distinction and the simple-complex distinction. Briefly, the puzzle is as follows. Hume appears to endorse a very strong version of nominalism—the thesis that only particulars, and not qualities or relations, exist. The distinctions that he employs in pursuing the science of human nature, however, only have the explanatory force that they do if they represent the real qualities and relations among our perceptions. Thus, I take Hume to be a kind of scientific realist: he is a nominalist about that which is represented by the general terms employed by the vulgar and false philosophy, but believes that those represented by the general terms of the science of human nature are in fact robustly real. The details of that solution to this puzzle and of this interpretation of Hume’s understanding of the science of human nature will not be entirely worked out until the end of Chapter 5 because presenting it in its entirety requires understanding a great many of the intricacies of Hume’s philosophical system, and how these all function together. Suffice it to say for now that what I will argue over the course of this study is that Hume employs a three-tier system consisting of a picture theory of mental representation, an account of reason’s analogical extension of perceptible models into theoretical representations, and a linguistic mechanism of ontological commitment. We can begin with the first of these.¹

Hume’s Theory of Mental Representation

As is generally acknowledged, there is a great deal of textual support for the thesis that there is a very close link between Hume’s notion of copying and his theory of mental representation.² The most straightforward way of drawing this link—defended by Cohon and Owen, “Hume on Representation”— is simply to identify them.

Representation _CO: a perception represents only that of which it is a copy.

The key notion here is that of being a copy, and Hume is fairly clear about just what this entails. For x to be a copy of y requires that two conditions be met. These conditions are each necessary, and together are jointly sufficient, for x to be a copy of y. The first condition is that x must be caused by y. Of course, ‘cause’ must be construed in the proper Humean way here—more on this in Chapter 5—so that for x to be caused by y is for x and y to be constantly conjoined, and for y to always precede x. So, for example, when Hume sets out to prove the Copy Principle in the opening pages of the Treatise—the thesis that all simple ideas are copies of some simple impression—he observes that exactly these two parts of the causal condition are met.

I first make myself certain, by a new review, of what I have already asserted, that every simple impression is attended with a correspondent idea, and every simple idea with a correspondent impression. From this constant conjunction of resembling perceptions I immediately conclude, that there is a great connexion betwixt our correspondent impressions and ideas, and that the existence of one has a considerable influence upon that of the other. Such a constant conjunction, in such an infinite number of instances, can never arise from chance; but clearly proves a dependence of the impressions on the ideas, or of the ideas on the impressions. That I may know on which side this dependence lies, I consider the order of their first appearance; and find by constant experience, that the simple impressions always take the precedence of their correspondent ideas, but never appear in the contrary order.

T 1.1.1.8; SBN 4

Correspondent impressions and ideas are constantly conjoined, and the former always precede the latter. Thus, Hume can conclude that impressions are the cause of ideas (in the proper Humean sense of ‘cause’).

The second condition that must be met for x to be a copy of y is that x must exactly resemble y. Again, here is Hume in the opening pages of the Treatise offering evidence that this condition is met in the case of ideas and impressions.

The first circumstance, that strikes my eye, is the great resemblance betwixt our impressions and ideas in every other particular, except their degree of force and vivacity.

T 1.1.1.3; SBN 2

Of course, Hume goes on to limit his resemblance thesis to simple ideas and impressions only, and so correspondingly limits the Copy Principle to just these as well, which caveat will become important in a moment.

Before that, though, notice that what we have just been examining is Hume’s defense of the Copy Principle, the thesis that all simple ideas are copies of some simple impression. That thesis is distinct from Representation _CO insofar as the Copy Principle concerns only the causal relation between simple impressions and ideas and the relation of what we might call their pictorial character. It will be important to carefully distinguish these two principles. I will explain. Consider the following picture.

The pictorial character of this picture consists of four black lines of equal length arranged at ninety-degree angles to one another against a white background. That is in what the picture consists. For another picture to exactly resemble this one, it would also have to consist in four lines of this length arranged at ninety-degree angles to one another against a white background. The pictorial character of an image, including impressions and ideas, is constituted entirely by the intrinsic features of that image.

This is a point commonly made about Hume’s exact resemblance thesis in order to explicate the notions of force and vivacity, which are not part of the pictorial character of perceptions precisely because they are not intrinsic features of a perception.³ What concerns us here, however, is a slightly different contrast. Notice that in describing the image above, we made no reference to what that image represents. That is, we described the intrinsic features of that picture, but did not mention, for instance, that it is a picture of a building as seen from directly above, or a book seen from straight on, etc. We can call what a picture is a picture of the representational content of that image, and it will be important for what follows to notice that it is, pre-theoretically, possible for the pictorial character of an image and the representational content of that same image to come apart. For instance, there are abstract paintings that certainly have pictorial character (a bunch of red, yellow, and blue paint splashes on a white canvas), but which do not have any representational content (these paintings are not paintings of anything). Conversely, in typical cases, the pictorial character of a written or spoken word is, in a sense, irrelevant to what it represents—hieroglyphics and onomatopoeia aside—(such words are not iconic representations; ‘dog’ does not look like a dog), but do have representational content (they are representations).⁴ So, Hume’s Copy Principle states that all ideas are copies of impressions, i.e., that all ideas are caused by, and have exactly the same pictorial character as, some corresponding impression. Important for us to note is that, as formulated here, the Copy Principle does not speak at all towards the representational content of impressions or ideas. It is merely a thesis concerning the causal relations between impressions and ideas and the relation of their pictorial character. Representation _CO adds to the Copy Principle that not only are all ideas copies of impressions, but also that an idea represents only that of which it is a copy.⁵

Figure 1.1

As evidence for this understanding of Hume, Cohon and Owen cite Hume’s use of the idiom of representation throughout his introduction and defense of the Copy Principle in the opening pages of the Treatise and the use to which he appears to put Representation _CO in his arguments thereafter. In fact, though, as it stands, Representation _CO cannot be right for reasons that Hume himself explicitly acknowledges, although a small change to it that preserves its spirit if not its letter will suffice to ameliorate the problem. As we just noted, Hume restricts the Copy Principle to simple impressions and ideas. The content of this claim from early on in the Treatise is only that every simple idea is copied from some simple impression.⁶ Correspondingly, then, if it is only simple ideas that are copied from simple impressions, Representation _CO must similarly apply only to simples. That is, since Representation _CO states that a perception represents only that of which it is a copy, and only simple ideas are copies of anything, then it would seem to follow that only simple ideas represent anything. This, however, cannot be right.

First of all, any plausible theory of mental representation must to be able to account for the representational content of thoughts of complex items such as that of a dog, a person kicking a ball, etc. Hume clearly does so by casting such thoughts of complexes as themselves being complex ideas, and so he must have some account of how such ideas represent what they do. He certainly writes as if he does.

I can imagine myself such a city as the New Jerusalem, whose pavement is gold and walls are rubies, tho’ I never saw any such. I have seen Paris; but shall I affirm I can form any such an idea of that city, as will perfectly represent all its streets and houses in their real and just proportions?

T 1.1.1.5; SBN 3

This is only one of a vast number of instances in which Hume indicates that he takes complex ideas to represent. This quotation also brings out a second problem with Representation _CO. If a perception represents only that of which it is a copy, then no perception can ever mis represent. If a perception represents only that of which it is a copy, then the object of any perception that represents at all is always guaranteed to exist (since it had to be copied in order to be represented), and so such representations can never go wrong. As we saw in the above quotation, Hume is clearly aware of the phenomenon of misrepresentation: we can represent New Jerusalem even though it has never existed, and our representation of Paris does not correspond exactly to the details of the actual city.

What is also indicated by the above quotation is that Hume takes these two problems to be connected: it is our ability to represent via complex ideas that leads to our making such errors. Recall the context in which Hume writes the above. He has just proposed for the first time that all of his ideas exactly resemble some impression. He then notices these two kinds of examples, and uses the distinction he has previously drawn between simple and complex ideas to restrict the scope of his claim to just simple ideas. The implication certainly seems to be that it is the fact that such ideas are complex that keeps them from exactly resembling some impression, and that this is not the case with simple ideas. Simple ideas cannot misrepresent; only complex ideas can.

Here, then, is a proposal for how to emend Representation _CO to account for complex and misrepresentation, while keeping copying at the core of Hume’s account. A simple perception represents only that of which it is a copy. Notice that a complex perception is nothing more than an arrangement of simple perceptions. So, take seriously the Humean slogan that a representation of a complex is nothing more than a complex of representations. That is, a complex perception represents the simple objects that are represented by its simple parts as being arranged in the way that those simple parts are arranged in it. Consider, for instance, Hume’s account of the origin of our representations of spatial complexes.

The table in front of me is alone sufficient by its view to give me the idea of extension. This idea, then, is borrow’d from, and represents some impression, which this moment appears to the senses. But my senses convey to me only the impressions of colour’d points, dispos’d in a certain manner. If the eye is sensible of any thing farther, I desire it may be pointed out to me. But if it be impossible to show any thing farther, we may conclude with certainty, that the idea of extension is nothing but a copy of these colour’d points, and of the manner of their appearance.

T 1.2.3.4; SBN 34, emphasis mine

Our complex idea of a spatial complex comes to represent the spatial complex that it does by being a collection of simple ideas of colored points arranged in a way that exactly resembles the arrangements of the spatial complex being represented. We represent the relation that some simple impressions stand in to one another by arranging simple representations of each of these impressions into the same relation. We represent a as being next to b by placing an idea of a next to an idea of b. The idea of a spatial complex is nothing more than a spatial comple...

Table of contents

• Cover
• Title
• Copyright
• Dedication
• Contents
• Acknowledgments
• Notes on Hume’s Texts
• Introduction
• 1 Two Case Studies: The Impression-Idea and Simple-Complex Distinctions
• 2 Hume’s Scientific Realism
• 3 The Course of Science: Substance, Language, and Reason
• 4 The Science of Body
• 5 Necessary Connection and Substantial Explanation
• 6 Explanation and Personal Identity in the Appendix
• Bibliography
• Index