hume's empiricism

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Philo of Science

Class Notes, page 91 of 3

D VID HUME

The most important philosopher ever to write in English, David Hume (1711-1776) — the last

of the great triumvirate of “British empiricists” — was also well-known in his own time as an

historian and essayist. A master stylist in any genre, Hume’s major philosophical works — A

Treatise of Human Nature (1739-1740), the Enquiries concerning Human Understanding

(1748) and concerning the Principles of Morals (1751), as well as the posthumously published Dialogues concerning

Natural Religion (1779) — remain widely and deeply influential.

Although many of Hume’s contemporaries denounced his writings as works of scepticism and atheism, his

influence is evident in the moral philosophy and economic writings of his close friend Adam Smith. Hume also

awakened Immanuel Kant from his “dogmatic slumbers” and “caused the scales to fall” from Jeremy Bentham’s

eyes. Charles Darwin counted Hume as a central influence, as did “Darwin’s bulldog,” Thomas Henry Huxley. The

diverse directions in which these writers took what they gleaned from reading Hume reflect not only the richness

of their sources but also the wide range of his empiricism. Today, philosophers recognize Hume as a precursor of

contemporary cognitive science, as well as one of the most thoroughgoing exponents of philosophical naturalism.

(Excerpt from Ted Morris’ “David Hume’s Life and Works” in The Hume Society)

[http://www.humesociety.org/about/HumeBiography.asp]

Hume's Scepticism

David Hume extended and made consistent Locke's sceptical approach to the possibility of a necessaryknowledge of nature. Hume consistently denied that a knowledge of atomic configurations and interactions-even if itcould be achieved-would constitute a necessary knowledge of nature. According to Hume, even if our faculties were“fitted to penetrate into the internal fabric” of bodies, we could gain no knowledge of a necessary connectedness

among phenomena. The most we could hope to learn is that certain configuration s and motions of atoms have beenconstantly conjoined with certain macroscopic effects. But knowing that a constant conjunction has been observed isnot the same thing as knowing that a particular motion must produce a particular effect. Hume held that Locke waswrong to suggest that if we knew the atomic configuration of gold then we would understand without trial that thissubstance must be soluble in aqua regia.

Hume's denial of the possibility of a necessary knowledge of nature was based on three explicitly stated premisses: (1) all knowledge may be subdivided into the mutually exclusive categories “relations of ideas” and“matters of fact”; (2) all knowledge of matters of fact is given in, and arises from, sense impressions; and (3) anecessary knowledge of nature would presuppose knowledge of the necessary connectedness of events. Hume'sarguments in support of these premisses were widely influential in the subsequent history of the philosophy ofscience.

Subdivision of Knowledge

Hume maintained that statements about relations of ideas and statements about matters of fact differ in tworespects. The first respect is the type of truth-claim that can be made for the two types of statements. Certain state-ments about relations of ideas are necessary truths. For instance, given the axioms of Euclidean geometry, it couldnot be otherwise than that the sum of angles of a triangle is 180 degrees. To affirm the axioms and deny the theoremis to construct a self-contradiction. Statements about matters of fact, on the other hand, are never more thancontingently true. The denial of an empirical statement is not a self-contradiction; the state of affairs described couldhave been otherwise.

The second point of difference is the method followed to ascertain the truth or falsity of the respective types ofstatements. The truth or falsity of statements about relations of ideas is established independently of any appeal to



Philo of Science


empirical evidence. Hume subdivided statements about relations of ideas into those which are intuitively certain andthose which are demonstratively certain. For example, the axioms of Euclidean geometry are intuitively certain;their truth is established upon examination of the meanings of their component terms. The Euclidean theorems aredemonstratively certain; their truth is established by demonstrating that they are deductive consequences of theaxioms. Any appeal to the measurement of figures drawn on paper or in sand is wholly irrelevant. Hume declaredthat “though there never were a circle or triangle in nature, the truths demonstrated by Euclid would for ever retaintheir certainty and evidence.”

The truth or falsity of statements about matters of fact, on the other hand, must be established by an appeal toempirical evidence. One cannot establish the truth of a statement that something has happened, or will happen,simply by thinking about the meaning of words.

Hume thus effected a demarcation of the necessary statements of mathematics from the contingent statements ofempirical science, thereby sharpening Newton's distinction between a formal deductive system and its application toexperience. Albert Einstein later rephrased Hume's insight as follows: “as far as the laws of mathematics refer toreality, they are not certain; and as far as they are certain, they do not refer to reality.” Hume's demarcation placed aroadblock in the path of any naive Pythagoreanism which seeks to read into nature a necessary mathematicalstructure.

The Principle of Empiricism

Hume maintained that Descartes was wrong to hold that we possess innate ideas of mind, God , body, and world.According to Hume sense impressions are the sole source of knowledge of matters of fact. * He thus echoedAristotle's dictum that there is nothing in the intellect which was not first in the senses. Hume's version was that “allour ideas are nothing but copies of our impressions, or, in other words, that it is impossible for us to think of am,thing, which we have not antecedently felt, either by our external or internal senses.”

Hume's thesis is both a psychological hypothesis about the genesis of empirical knowledge and a logicalstipulation of the range of empirically significant concepts. Hume restricted empirically significant concepts to thosewhich can be "derived from" impressions." Thus stated, Hume's criterion is quite vague. Elsewhere in the Enquiry

( Enquiry Concerning Human Understanding) , he suggested that the role of the mind in generating knowledge isrestricted to the compounding, transposing, augmenting, or diminishing, of the ideas “copied from” impressions.Presumably, any concept is excluded which is neither a “copy” of an impression nor the result of a process ofcompounding, transposing, augmenting, or diminishing. Concepts excluded by Hume himself include “a vacuum”,“substance”, “perduring selfhood”, and “necessary connectedness of events”.

Hume's analysis has been interpreted as reinforcing Baconian inductivism, a tradition that perhaps owes as muchto Hume's epistemological investigations as to the counsel of Francis Bacon himself. Thus interpreted, Hume has

been held to claim that science begins with sense impressions and can encompass only those concepts which are“constructed” somehow out of sense data. Such a view is consistent with the Method of Analysis, but not with

Newton's axiomatic method.But although this reading of Hume has been influential it fails to do justice to the complexity of Hume's position.

For Hume acknowledged that the formulation of comprehensive theories, such as Newton's mechanics, is achieved by a creative insight not reducible to a “compounding, transposing, augmenting, or diminishing” of ideas “copiedfrom” impressions. What he did deny, however, is that any such theories could achieve the status of necessary truth.

Analysis of Causation

Bacon and Locke had discussed the question of a necessary knowledge of nature from a scholastic standpoint.

Both had recommended the study of the coexistence of properties. Hume shifted the search for necessary empiricalknowledge to sequences of events. He asked whether a necessary knowledge of such sequences was possible, anddecided that it was not. Hume held that to establish a necessary knowledge of a sequence of events one would haveto prove that the sequence could not have been otherwise. But Hume pointed out that it was not a self-contradictionto affirm that although every A has been followed by a B, the next A will not be followed by a B.

* Hume included among “sense impressions” desires, volitions, and feelings, as well as visual, auditory, tactile, and olfactory

data.



Philo of Science


Hume undertook to examine our idea of a “causal relation”. He noted that if we mean by a ‘causal relation’ both‘constant conjunction’ and ‘necessary connection’, then we can achieve no causal knowledge at all. This is becausewe have no impression of any force or power by means of which an A is constrained to produce a B. The most thatwe can establish is that events of one type invariably have been followed by events of a second type. Humeconcluded that the only “causal” knowledge that we can hope to achieve is a knowledge of the de facto associationof two classes of events.

Hume conceded that we do feel that there is something necessary about many sequences. According to Hume,this feeling is an impression of the “internal sense”, an impression derived from custom. He declared that “after arepetition of similar instances, the mind is carried by habit, upon the appearance of one event, to expect its usualattendant, and to believe that it will exist.” Of course, the fact that the mind comes to anticipate a B upon theappearance of an A is no proof that there is a necessary connection between A and B.

Consistent with this analysis, Hume stipulated definitions of `causal relation' both from an objective and from asubjective standpoint. Objectively considered, a causal relation is a constant conjunction of the members of twoclasses of events; subjectively considered, a causal relation is a sequence such that, upon appearance of an event ofthe first class, the mind is led to anticipate an event of the second class.

These two definitions appear both in the Treatise ( A Treatise of Human Nature) and in the Enquiry. However, inthe Enquiry, Hume inserted after the first definition the following qualification: “or in other words where, if the firstobject had not been, the second never had existed.” Replacing the term ‘object’ by ‘event’, which is consistent withHume's own usage, it is evident that this new definition is not equivalent to the first definition. For instance, in thecase of two similar pendulum clocks arranged to be go degrees out of phase, the ticks of the two clocks are

constantly conjoined, but this does not imply that if the pendulum of clock 1 were arrested, then clock 2 would ceaseto tick.

Hume's inclusion of this qualification in the Enquiry may indicate that he was not quite satisfied to equate causalrelation and de facto regularity. Another likely indication of his uneasiness is the fact that he included in theTreatise, tersely and without comment, a list of eight “Rules by which to judge of Causes and Effects”. Among theserules are versions of the Methods of Agreement, Difference, and Concomitant Variations, later made famous byMill.

The Method of Difference, in particular, enables the investigator to judge causal connection upon observation of just two instances. It would seem, in this case, that Hume contradicted his “official position” that we term a relation“causal” only upon experience of a constant conjunction of two types of events. Hume denied this. He maintainedthat although belief that a succession of events is a causal sequence may arise even after a single observation of thesequence, the belief nevertheless is a product of custom. This is because the judgement of causal connection in suchcases depends implicitly on the generalization that like objects in like circumstances produce like effects. But this

generalization itself expresses our expectation based on extensive experience of constantly conjoined events. Henceour belief in a causal connection invariably is a matter of habitual expectation.

Having thus accounted for the origin of our belief in causal connection, Hume was quick to point out that noappeal to the regularity of past experience can guarantee fulfillment of our expectations about the future. He statedthat “it is impossible, therefore, that any arguments from experience can prove this resemblance of the past to thefuture; since all these arguments are founded on the supposition of that resemblance.” Hence it is not possible toachieve a demonstrative knowledge of causes from premisses which state matters of fact.

Hume thus completed a sweeping attack on the possibility of a necessary knowledge of nature. Such knowledgewould have to be either immediate or demonstrative. Hume had shown that no immediate knowledge of causes is

possible, for we have no impression of necessary connection. He also had shown that it is not possible to achieve ademonstrative knowledge of causes, either from premisses which state a priori true relations of ideas, or from

premisses which state matters of fact. There seemed to be no further possibility. No scientific interpretation canachieve the certainty of a statement such as “the whole is greater than each of its parts.” Probability is the only

defensible claim that can be made for scientific laws and theories.Although Hume's scepticism was apprehended as a threat to science by those who were not satisfied with “merely probable” knowledge, Hume himself was quite ready to rely on the testimony of past experience. On the practicallevel, Hume was not a sceptic. He declared that custom, then, is the great guide of human life. It is that principlealone which renders our experience useful to us ... Without the influence of custom, we should be entirely ignorantof every matter of fact beyond what is immediately present to the memory and senses.

Source: John Losee, A Historical Introduction to the Philosophy of Science, 4th ed. (Oxford University Press, 2001).

hume's empiricism

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