An Enquiry concerning Human Understanding (World's Classics)

by David Hume

Despite this variety of speculation, these thinkers all shared some important assumptions, notably a view of the world as created by divine reason, and—relatedly—as potentially ‘intelligible’ to human reason. Hume’s special significance is as the first great philosopher to question both of these pervasive assumptions, and to build an epistemology and philosophy of science that in no way depend on either of them. Over a century before Charles Darwin’s Origin of Species of 1859, Hume argued powerfully that human reason is fundamentally similar to that of the other animals, founded on instinct rather than quasi-divine insight into things. Hence science must proceed by experiment and systematization of observations, rather than by metaphysical theorizing or a priori speculation.

What makes a truth a priori is that it can be justified without appeal to experience, purely by thinking about the ideas involved. Matters of fact, by contrast, can be known to be true (or to be false) only by consulting experience.

Demonstrative reasoning is what can be loosely called ‘deductive’ reasoning,21 in which the steps of the argument proceed with absolute certainty based on the logical relations between the ideas concerned (e.g. the kind of argument used in mathematics, such as the proof of Pythagoras’ Theorem). Factual reasoning—which Hume also calls ‘moral’ and Locke had called ‘probable’—is now commonly called ‘inductive’ inference, encompassing all sorts of everyday reasoning in which we draw apparently reasonable (but less than logically certain) conclusions based on our personal experience, testimony, our understanding of how people and things behave, and so forth.

The necessity of any action, whether of matter or of mind, is not, properly speaking, a quality in the agent, but in any thinking or intelligent being, who may consider the action. (E 8.22 endnote [F]) Some recent interpreters have cast doubt on the extent to which passages such as these reflect a genuine subjectivism on Hume’s part.25 But in terms of its influence on epistemology, metaphysics, and the philosophy of science, this ‘anti-realism’ about causation, along with his inductive scepticism, constitutes his most prominent legacy.

Thus a priori demonstration is limited to the abstract realm of ideas, but only in mathematics are our ideas sufficiently precise to make demonstrative argument genuinely fruitful (E 12.27). The upshot of all this is to limit the worthwhile fields of investigation to mathematics (which is a priori but concerns only relations of ideas) and inductive empirical science (which concerns matters of fact but is uncertain and empirical). Any work that purports to transcend these limits, by establishing matters of fact with demonstrative certainty—what Immanuel Kant would later call ‘synthetic a priori knowledge’—can therefore be roundly condemned, as Hume expresses in his famous concluding paragraph: 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 containing quantity or 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. (E 12.34)

Be a philosopher; but, amidst all your philosophy, be still a man.

all our ideas or more feeble perceptions are copies of our impressions or more lively ones.*

To me, there appear to be only three principles of connexion among ideas, namely, Resemblance, Contiguity in time or place, and Cause or Effect.

ALL the objects of human reason or enquiry may naturally be divided into two kinds, to wit, Relations of Ideas, and Matters of Fact.

All reasonings concerning matter of fact seem to be founded on the relation of Cause and Effect. By means of that relation alone we can go beyond the evidence of our memory and senses.

All reasonings may be divided into two kinds, namely demonstrative reasoning, or that concerning relations of ideas, and moral reasoning,* or that concerning matter of fact and existence.

Nor need we fear, that this philosophy, while it endeavours to limit our enquiries to common life, should ever undermine the reasonings of common life, and carry its doubts so far as to destroy all action, as well as speculation. Nature will always maintain her rights, and prevail in the end over any abstract reasoning whatsoever. Though we should conclude, for instance, as in the foregoing section, that, in all reasonings from experience, there is a step taken by the mind, which is not supported by any argument or process of the understanding; there is no danger, that these reasonings, on which almost all knowledge depends, will ever be affected by such a discovery. If the mind be not engaged by argument to make this step, it must be induced by some other principle of equal weight and authority; and that principle will preserve its influence as long as human nature remains the same. What that principle is, may well be worth the pains of enquiry.

This principle is CUSTOM or HABIT.* For wherever the repetition of any particular act or operation produces a propensity to renew the same act or operation, without being impelled by any reasoning or process of the understanding; we always say, that this propensity is the effect of Custom. By employing that word, we pretend not to have given the ultimate reason of such a propensity. We only point out a principle of human nature, which is universally acknowledged, and which is well known by its effects.

All inferences from experience, therefore, are effects of custom, not of reasoning8. 43 [6] Custom, then, is the great guide of human life.* It is that principle alone, which renders our experience useful to us, and makes us expect, for the future, a similar train of events with those which have appeared in the past. Without the influence of custom, we should be entirely ignorant of every matter of fact, beyond what is immediately present to the memory and senses.

disquisitions,

No conclusions can be more agreeable to scepticism than such as make discoveries concerning the weakness and narrow limits of human reason and capacity.

Thus for instance, in the human body, when the usual symptoms of health or sickness disappoint our expectation; when medicines operate not with their wonted powers; when irregular events follow from any particular cause; the philosopher and physician are not surprized at the matter, nor are ever tempted to deny, in general, the necessity and uniformity of those principles, by which the animal oeconomy is conducted. They know, that a human body is a mighty complicated machine: That many secret powers lurk in it, which are altogether beyond our comprehension: That to us it must often appear very uncertain in its operations: And that therefore the irregular events, which outwardly discover themselves, can be no proof, that the laws of nature are not observed with the greatest regularity in its internal operations and government.

A wise man, therefore, proportions his belief to the evidence.

There is no enthusiasm* among philosophers; their doctrines are not very alluring to the people; and no restraint can be put upon their reasonings, but what must be of dangerous consequence to the sciences, and even to the state, by paving the way for persecution and oppression in points, where the generality of mankind are more deeply interested and concerned.

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 or 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.

Θεоς απо μηχαυης: Greek phrase equivalent to the more familiar Latin deus ex machina, meaning ‘god out of a machine’. It refers to the practice used by some classical playwrights, of resolving a plot (often rather implausibly) through the intervention of a god, lowered onto the stage by a mechanism.