The Evolution of Modern Metaphysics: Making Sense of Things (26 page)

’Tis evident that all the sciences have a relation, greater or less, to human nature…. Even
Mathematics, Natural Philosophy, and Natural Religion
, are in some measure dependent on the science of
MAN
; since they lie under the cognizance of men, and are judged of by their powers and faculties. ’Tis impossible to tell what changes and improvements we might make in these sciences were we thoroughly acquainted with the extent and force of human understanding, and cou’d explain the nature of the ideas we employ, and of the operations we perform in our reasonings….

There is no question of importance, whose decision is not compriz’d in the science of man; and there is none, which can be decided with any certainty, before we become acquainted with that science. In pretending therefore to explain the principles of human nature, we in effect propose a compleat system of the sciences, built on a foundation almost entirely
new, and the only one upon which they can stand with any security. (pp. xv–xvi, emphasis in original; cf.
Enquiry
, §I)
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Metaphysics is entirely acceptable, then, provided that it consists in an experimental science of human nature.

(Notice, incidentally, the deep structural affinity between what Hume aspires to do and what Descartes aspired to do. The project, in each case, is to provide a firm foundation for the sciences by making sense of how we make sense of things. In each case this means arriving at a set of beliefs about how we arrive at our beliefs about the world from our ‘perceptions’, a set of beliefs that must apply, in particular, to the execution of this very project. (See
Ch. 1
, §4, and the comparison there with Quine’s naturalized epistemology.) But of course, there are vital differences between Hume’s execution of the project and Descartes’. Descartes took himself to be trafficking in indubitable
a priori
insights into where we stand in relation to things and how we make sense of them. Hume believes that there is only one route to an understanding of where we stand in relation to things and how we make sense of them: the ever fallible investigation, through observation and experiment, of human nature.)

But can the study of human nature, at any level of generality, really do duty for metaphysics? On my definition, perhaps; but is there not reason now to regard that definition as too gross a departure from ordinary usage?

I do not think so. When Hume explores the processes whereby we acquire our idea of a (causally) necessary connection, and reflects on how much, in our talk of causation, registers our reaction to the regularities that we observe, rather than the regularities themselves, then he is engaged in what would by any reckoning count as the metaphysics of causation. Likewise when he explores the psychological mechanisms that underpin our talk of ‘external’ objects, or our talk of personal identity (though it should be noted, where these latter topics are concerned, that his discussions are pretty much confined to the
Treatise
, which is a decidedly more metaphysical work than the
Enquiry
).

Very well. There may be good reason to regard some of Hume’s investigations into matters of fact as a significant contribution to metaphysics. But unless the same can be said for his investigations into relations of ideas, then must he not be regarded, as he so often is regarded, as eschewing standard traditional metaphysics? For if the distinction between relations of ideas and matters of fact is to be granted at all, then the extreme generality of metaphysics must surely mean that its principal home is the former, where
not only can it issue in results about the sense that we succeed in making of things, as revealed in the way we acquire and marshal our ideas, but it can also issue in results about the sense that things make, as revealed in the ideas themselves. Yet Hume notoriously refuses to allow that there can be any interesting or important relations of ideas beyond the realm of mathematics. It is in this spirit that he famously writes, in the final paragraph of the
Enquiry
:

When we run over libraries, persuaded of these principles, what havoc must we make? If we take in our hand any volume; of divinity or school metaphysics, for instance; let us ask,
Does it contain any abstract reasoning concerning quantity and number?
No.
Does it contain any experimental reasoning concerning matter of fact and existence?
No. Commit it then to the flames: for it can contain nothing but sophistry and illusion. (p. 165, emphasis in original)

No doubt any sophistry and illusion that we encounter will be due to the fact that someone, at some point, has attempted to make sense of what is transcendent, in one or other of the ways that we have already seen Hume decry. Even so, he is offering, in this paragraph, a new criterion for such sophistry and illusion. He is saying that they reside wherever people try to engage in enquiries that are neither mathematical nor factual (in a suitably Humean sense of ‘factual’). And, in the light of that, no amount of fast and loose play with the definition of ‘metaphysics’ can prevent his work from still appearing to be what it has always appeared to be: an attack, if not on metaphysics
per se
, then at least on metaphysical hubris, an attack on any attempt to make highly general sense of things by establishing substantive
a priori
non-mathematical necessities.

5. Metaphysics as More Than an Experimental Science of Human Nature

Why does Hume have such a restricted conception of relations of ideas? Mathematics itself testifies to the fact that there can be non-trivial connections between our ideas – indeed, substantive connections, provided that ‘substantive’ is understood in a sufficiently modest psychological way. If there can be such connections ‘concerning quantity and number’, then why not concerning causation, or free will, or any of the other items traditionally reckoned to be of metaphysical concern? Indeed, does Hume not do himself a disservice by overlooking some of his own substantive non-factual conclusions about just such topics?
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Here is what Hume says:

It seems to me, that the only objects of the abstract sciences are quantity and number, and that all attempts to extend this more perfect species of knowledge beyond these bounds are mere sophistry and illusion. As the component parts of quantity and number are entirely similar, their relations become intricate and involved; and nothing can be more curious, as well as useful, than to trace, by a variety of mediums, their equality or inequality through their different appearances. But as all other ideas are clearly distinct and different from each other, we can never advance farther, by our utmost scrutiny, than to observe this diversity, and, by an obvious reflection, pronounce one thing not to be another. Or if there be any difficulty in these decisions, it proceeds entirely from the undeterminate meaning of words, which is corrected by juster definitions. That
the square of the hypothenuse is equal to the squares of the other two sides
, cannot be known, let the terms be ever so exactly defined, without a train of reasoning and enquiry. But to convince us of this proposition,
that where there is no property, there can be no injustice
, it is only necessary to define the terms, and explain injustice to be a violation of property. (
Enquiry
, p. 163, emphasis in original)
³⁸

In the
Treatise
there is more detail. Hume tells us there that the only relations among our (simple?) ideas that can issue in relations of ideas, other than ‘proportions in quantity or number’, are ‘resemblance’, ‘contrariety’, and ‘degrees in quality’, and that these are all ‘discoverable at first sight’ (p. 70; see further the rest of I.iii.1).

Hume’s contention, then, is as follows. Outside mathematics, our (simple?) ideas are more or less independent of one another. The only relevant relations that they enter into are relations whose obtaining is always blatant even given such independence, for instance the relation of comparative intensity which obtains between an idea of burning heat and an idea of gentle warmth. Hence there is no scope for our non-mathematical ideas to feature in necessary truths that are interesting, surprising, or in any other sense ‘substantive’.

It is a contention which, within Hume’s own framework, can be refuted only by the specification of a counterexample: either some relation that he has overlooked or some unexpected hidden complexity in one of the relations that he has considered. And, I think we must concede, there are no obvious counterexamples. Suppose, for instance, that we were to turn his own work against him in the way suggested above, by invoking some of the connections that he himself has established. He might well reply that all he has done, as in the example concerning injustice, is to define certain key terms – by indicating the meaning already attaching to them, where they already had a clear meaning, and by assigning a meaning to them where they did not – whereafter nothing more was needed to establish these connections than a few trivial steps of logic.
³⁹

But to concede that there are no obvious counterexamples is not to concede much. Part of the reason why there are no obvious counterexamples is that it is not obvious what would count as a counterexample. It is not obvious
even
within Hume’s framework, never mind that every feature of that framework, most notably the very dichotomy between relations of ideas and matters of fact, is itself contestable. Thus reconsider the list of relations that Hume tells us can issue in relations of ideas. That this is an exhaustive list is itself, presumably, supposed to be a matter of (introspectively testable) fact, about the human mind. But we would surely need more guidance in construing these relations before we could be confident that we would recognize a counterexample when we encountered it. Hume tells us, for instance, that ‘no two ideas are in themselves contrary, except those of existence and non-existence’ (
Treatise
, p. 15). This means, in particular, that the idea of red and the idea of blue are not ‘in themselves contrary’. That there may be interesting ways of explicating the relation of contrariety to allow for this I shall not dispute. That the relation
needs
to be explicated is surely beyond dispute.
⁴⁰
Or again, suppose we found what we took to be some substantive non-mathematical relation of ideas, say that no barber can shave all and only the men in his village who do not shave themselves.
⁴¹
It would always be open to Hume either simply to deny that there was any substantiveness there or to attribute the substantiveness to a kind of applied mathematics of concepts.
⁴²

But be the refutation of Hume’s contention as it may, we should consider what motivates it. Our own chief concern is with its implications
concerning metaphysics. But that is not, I suggest, Hume’s chief concern. Hume’s chief concern, I suggest, is manifest in that famous passage from the
Treatise
in which he expresses his commitment to the ‘is’/‘ought’ distinction:

In every system of morality, which I have hitherto met with, I have always remark’d, that the author proceeds for some time in the ordinary way of reasoning …; when of a sudden I am surpriz’d to find, that instead of the usual copulations of propositions,
is
, and
is not
, I meet with no proposition that is not connected with an
ought
, or an
ought not
. This change … is of the last consequence. For as this
ought
, or
ought not
, expresses some new relation or affirmation, ’tis necessary that it shou’d be observ’d and explain’d; and at the same time that a reason should be given, for what seems altogether inconceivable, how this new relation can be a deduction from others, which are entirely different from it. (
Treatise
, p. 469, emphasis in original)

Hume, who is adamant that nothing short of a suitable feeling of approbation or disapprobation in someone could force him or her to subscribe to a prescriptive or evaluative statement, wants to allow no refuge to the idea that ‘a train of reasoning and enquiry’ could reveal some deep, unexpected connection between how things are and how they ought to be.
⁴³
But if I am right that this is Hume’s chief concern, then he must confront the possibility – a possibility on which we shall see Kant fasten tenaciously in the next chapter, albeit with his own different set of concerns – that there is a healthy baby in the bathwater that he has ejected.

This is a comment specifically about what scope there is for making a significant contribution to metaphysics that does not consist in establishing matters of fact, but consists rather in establishing relations of ideas. It leaves out of account the further important question of what scope there is for making a significant contribution to metaphysics that does not consist
either
in establishing matters of fact
or
in establishing relations of ideas – a question that arises even if we grant the Humean dichotomy between these. I have in mind something to which I adverted in §7 of the Introduction: the possibility of reflecting on the concepts that we have at our disposal and creating new ones to meet needs that the former do not.
⁴⁴
Hume himself is not averse to using familiar concepts to make radically new sense of things. I take it that this is a fair description of what he does when he says, in opposition to what anyone else at the time would say, that ‘[the] tie, which
connects [cause and effect] together[,] … lies merely in ourselves’ (
Treatise
, p. 266). But using radically new concepts to make radically new sense of things is one degree of innovation higher than that. And it is not obvious why it should not be a staple of good metaphysics.
⁴⁵