hume_s empiricism.pdf

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Philo of Science

D VID HUME

Hume's Scepticism

David Hume extended and made consistent Locke's sceptical approach to the possibility of

a necessary knowledge of nature. Hume consistently denied that a knowledge of atomic

configurations and interactions-even if it could be achieved-would constitute a necessaryknowledge 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 configurations and motions of atoms have been constantly conjoined with certain macroscopic

effects. But knowing that a constant conjunction has been observed is not the same thing as knowing that a

particular motion must produce a particular effect. Hume held that Locke was wrong to suggest that if we knew theatomic configuration of gold then we would understand without trial that this substance 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) a

necessary knowledge of nature would presuppose knowledge of the necessary connectedness of events. Hume's

arguments in support of these premisses were widely influential in the subsequent history of the philosophy of

science.

Subdivision of Knowledge

Hume maintained that statements about relations of ideas and statements about matters of fact differ in two

respects. 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 could

not be otherwise than that the sum of angles of a triangle is 180 degrees. To affirm the axioms and deny the theorem

is to construct a self-contradiction. Statements about matters of fact, on the other hand, are never more than

contingently true. The denial of an empirical statement is not a self-contradiction; the state of affairs described could

have been otherwise.The second point of difference is the method followed to ascertain the truth or falsity of the respective types of

statements. The truth or falsity of statements about relations of ideas is established independently of any appeal to

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 are

demonstratively 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 declared

that “though there never were a circle or triangle in nature, the truths demonstrated by Euclid would for ever retain

their certainty and evidence.”

The truth or falsity of statements about matters of fact, on the other hand, must be established by an appeal to

empirical 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 of

empirical science, thereby sharpening Newton's distinction between a formal deductive system and its application to

experience. Albert Einstein later rephrased Hume's insight as follows: “as far as the laws of mathematics refer to

reality, 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 mathematical

structure.

Class Notes, page 91 of 3


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Philo of Science

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 echoed

Aristotle's dictum that there is nothing in the intellect which was not first in the senses. Hume's version was that “all

our 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 logical

stipulation of the range of empirically significant concepts. Hume restricted empirically significant concepts to those

which 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 is

restricted 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 of

compounding, 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 much

to 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 “copied

from” 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 empirical

knowledge to sequences of events. He asked whether a necessary knowledge of such sequences was possible, and

decided that it was not. Hume held that to establish a necessary knowledge of a sequence of events one would have

to 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 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 because

we have no impression of any force or power by means of which an A is constrained to produce a B. The most that

we 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 association

of 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 a

repetition 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 the

appearance 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 two

classes of events; subjectively considered, a causal relation is a sequence such that, upon appearance of an event of

the first class, the mind is led to anticipate an event of the second class.

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

data.



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These two definitions appear both in the Treatise ( A Treatise of Human Nature) and in the Enquiry. However, in

the Enquiry, Hume inserted after the first definition the following qualification: “or in other words where, if the first

object had not been, the second never had existed.” Replacing the term ‘object’ by ‘event’, which is consistent with

Hume's own usage, it is evident that this new definition is not equivalent to the first definition. For instance, in the

case of two similar pendulum clocks arranged to be go degrees out of phase, the ticks of the two clocks areconstantly conjoined, but this does not imply that if the pendulum of clock 1 were arrested, then clock 2 would cease

to 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 the

Treatise, tersely and without comment, a list of eight “Rules by which to judge of Causes and Effects”. Among these

rules are versions of the Methods of Agreement, Difference, and Concomitant Variations, later made famous by

Mill.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 maintained

that 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 such

cases 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 stated

that “it is impossible, therefore, that any arguments from experience can prove this resemblance of the past to the

future; 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 knowledge

would 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 can

achieve the certainty of a statement such as “the whole is greater than each of its parts.” Probability is the onlydefensible 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 ignorant

of 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).


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