Philosophy

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David Hume lived from 1711-1776. In the history of Philosophy, he is usually

labeled as an empiricist and skeptic. He wrote An Enquiry Concerning Human

Understanding in 1748. He was Scottish and considered Edinburgh to be his home.

Hume held that direct sensory impressions are necessary for real experiences. He

would not have been satis�ed with activity-based solely on thinking or

contemplation.

There are two perceptions of the mind: (1) Impressions, direct experiences, which

can be Inner or Outer (outer- sensations, inner-emotions), and (2) Ideas, copies of

impressions, memories.

For Hume, the impressions have the most force and vivacity. “Force and vivacity”

is his test for reliable impressions, like Descartes’ “clear and distinct” test for

ideas. In Hume, the outer impressions are direct sensory experiences that are

certain experiences.

In comparison, the inner impressions have a special role to play in Hume’s ethics. For example, when we feel something is

wrong in our “gut,” we know it to be wrong.

Hume is interested in the fact that knowledge of the world around us can be doubtful, probabilistic, or based on odds.

Relations of Ideas and Matters of Fact

There are two kinds of knowledge, both expressed in propositions which can be known as true:

Relations of Ideas (true by virtue of de�nitions involved, “Bachelors are unmarried men.”)

Matters of Fact (statements of induction, prediction, cause and effect – “The sun will rise tomorrow”, “This bread

will nourish me.”)

This distinction between relations of ideas and matters of fact is often referred to as Hume’s Fork. The relations of ideas

may seem more certain, but they are only true in a trivial way. The matters of fact are where real new knowledge, or

scienti�c knowledge, could begin.

Habits and Customs

We assume the world will be in the future the same as it was in the past, but Hume points out that this can be problematic.

He presents counterexamples against what we assume are matters of fact. For example, the sun might not rise tomorrow,

especially if a catastrophic event like an asteroid hit the planet (like the one that caused the dinosaur extinction), and the

bread that looks perfectly nourishing to eat might actually contain a poison (arsenic, or botulism from a bad sourdough

starter for example.)

Hume argues that we must acknowledge the uncertainty in these “matters of fact” propositions, that cause and effect

relationships give us no direct impression of “cause” and so must be a custom or habit of thinking that we fall into. Rather

than assume our cause and effect relationships are a “necessary connection”, Hume says that they are merely “constant

conjunction.”

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Example: Billiard Balls

Hume argues that when we see billiard balls hitting each other and causing motion, we assume, or by force of habit, think

of them “causing” movements. There is no direct impression of a “cause” on its own. We should see the ball movements as

constantly conjoined, but not necessarily as ‘causes’ and effects. There could be another reason or cause that is why the

balls move – earthquakes, gravity, someone bumping into the table.

Skepticism and Induction

Skepticism and the Problem of Induction

Philosophical work in the theory of knowledge requires that we look for the reasons for our beliefs and evaluate

those reasons. If our reasons are bad reasons, or if we �nd that we have no reasons at all for our beliefs, then it

would seem that our beliefs are unjusti�ed. And unjusti�ed beliefs cannot qualify as knowledge.

Unless you are very unusual, you probably believe each of the following propositions:

The sun will rise tomorrow morning, just as it has risen every morning of your life.

The food you eat today will satisfy your hunger just as it has done in the past.

If you drop china teacups onto a cement �oor, they will break.

A person who didn't believe these things would be a skeptic indeed! But what are our reasons for believing these

things? According to David Hume, our reasons for these beliefs are inductive: since the sun has always risen in the

past, we are con�dent that it will rise tomorrow. Since food has always satis�ed hunger in the past, we do not

seriously doubt that it will do so today. Since fragile objects have not bounced like rubber in the past, we are quite

certain that they will not do so now.

But each of these inferences relies, according to Hume, on a crucial premise: Principle of the Uniformity of Nature -

The future will be like the past.

Hume does not deny that we believe that nature will be uniform in some respect. But he argues that we have no

good reasons to hold to this belief.

Hume's claim is quite radical: We all expect that the laws of physics will be the same tomorrow as they are today. It

would be surprising to discover that we have no good reasons to believe this, but this really is Hume's claim.

Hume does not recommend that we abandon induction once we discover that we cannot rationally justify it. We

cannot do that; we need to rely on inductive inferences if we are to go about our lives. But according to Hume, our

reliance on induction is not rational unless we can �nd some way to justify our con�dence in the Principle of the

Uniformity of Nature. And Hume �nds no way to justify this con�dence. He argues that we are just made in such a

way that we assume basic consistency; we cannot help assuming this substantive principle even though it cannot be

justi�ed by reason.



Can Inductive Reasoning Be Rationally Justi�ed

According to the Justi�ed True Belief theory, knowledge is justi�ed, true belief. We know something just in case we

believe it, our belief is justi�ed (perhaps because it is based on good reasons), and the proposition believed is true.

Knowledge requires "the circumstantial impossibility of error." That is, I can claim to know something only if, given

my circumstances, it is impossible that I be wrong about it. This is a very controversial requirement. Some

epistemologists contend that no belief is certain beyond the possibility of error.

David Hume was surprised to discover that he could not �nd adequate reasons to justify even simple beliefs. All of

these claims rely on, argued Hume, a kind of faith that the world is stable and that the laws of the Universe will not

change. And this belief, argued Hume, is one we cannot justify.

In this section, we will consider Hume's skeptical argument concerning induction.

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Reading Assignment: An Enquiry Concerning Human Understanding

Introduction

Hume's skeptical argument concerning induction is sophisticated and dif�cult. Part of the dif�culty is philosophical:

Hume's argument is complicated and clever, and it will take close attention to sort out the different strands. But part of

the dif�culty is due to language: Hume wrote in the late 18th century, and language has changed since then. Because of

this, Jonathan Bennett has carefully put portions of Hume's work into modern English. Bennett's restatement of Hume

sticks closely to the argument of the original text, but you may �nd it useful to compare Bennett's restatement to the

original.

This is dif�cult material, and you will surely need to read it more than once if you hope to understand it!

Some notes on reading Hume on induction:

When Hume speaks of the secret powers of objects, he simply means those properties that they have, but which we

cannot perceive simply by observation. These properties may be pretty ordinary and un-mysterious: for example, in

this sense, a bagel has a secret power to satisfy our hunger.

Hume claims that we have no rational basis for making inductive inferences. But he does not claim that it is

inappropriate or wrong for us to make such inferences - indeed, he recognizes that we need to make such inferences

all the time.

Some philosophical writing aims to explain confusing features of our world by showing that they are more readily

understandable than we might have supposed. But Hume has the opposite aim here: he uses a philosophical

argument to help us to recognize that the ordinary world and our ordinary habits of mind are much more surprising

and strange than we would otherwise have thought.

Inductive Generalizations and Predictions

Inductive generalizations and predictions all rely on the Principle of the Uniformity of Nature, the proposition that

the future will be like the past.

Inductive generalizations are arguments of the following form:

All observed X's have property Y.

Therefore, (probably) all Xs have property Y.

For example:

All observed swans are white.

Therefore (probably) all swans are white.

Inductive predictions have the following form:

All observed X's have property Y.

Therefore (probably) the Xs I observe in the future will have property Y.

For example:

All observed swans have been white.

Therefore (probably) the swans I see in the future will also be white.

Hume's claim is that all such arguments rely on an unstated premise that the future will be like the past. But this

unstated premise is itself in need of justi�cation, and when we examine it we �nd that it is unlikely that it could ever

be justi�ed. We have no good reason to believe in it at all.



Questions to Consider

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An Enquiry Concerning Human Understanding (part II)

[We] have not yet found an acceptable answer to the question that I initially asked. Each solution raises new questions

which are as hard to answer as the �rst one, and which lead us on to further enquiries. To the question What is the nature

of all our reasonings concerning matter of fact? the proper answer seems to be that they are based on the relation of

cause and effect. When it is further asked, What is the foundation of all our reasonings about cause and effect? we can

answer in one word, Experience. But if we persist with questions, and ask, What are inferences from experience based

on? this raises a new question which may be harder still. Philosophers - for all their air of superior wisdom - are given a

hard time by people who persist with questions, pushing them from every corner into which they retreat, �nally bringing

them to some dangerous dilemma [that is, a situation where they have to choose between two alternatives, each of which

seems wrong]. The best way for us to avoid such an embarrassment is not to claim too much in the �rst place, and even to

�nd the dif�culty for ourselves before it is brought against us as an objection. In this way we can make a kind of merit even

of our ignorance.

In this section I shall settle for something easy, offering only a negative answer to the question I have raised {about what

inferences from experience are based upon}. It is this: even after we have experience of the operations of cause and

effect, the conclusions we draw from that experience are not based on reasoning or on any process of the

understanding. I shall try to explain and defend this answer.

It must be granted that nature has kept us at a distance from all its secrets, and has allowed us to know only a few

super�cial qualities of objects, concealing from us those powers and principles on which the in�uence of the objects

entirely depends. Our senses tell us about the color, weight and consistency of bread; but neither the senses nor reason

can ever tell us about the qualities that enable bread to nourish a human body. Sight or touch gives us an idea of

the motion of bodies; but as for the amazing force which keeps a body moving for ever unless it collides with other bodies

- we cannot have the remotest conception of that. Despite this ignorance of natural powers and principles, however, we

always assume that the same sensible qualities will have the same secret powers, and we expect them to have the same

effects that we have found them to have in our past experience. If we are given some stuff with the color and consistency

of bread which we have eaten in the past, we do not hesitate to repeat the experiment {of eating it}, con�dently expecting

it to nourish and support us. {That is what we do every morning at the breakfast table: con�dently experiment with

bread-like stuff by eating it!} I would like to know what the basis is for this process of thought. Everyone agrees that a

thing's sensible qualities are not connected with its secret powers in any way that we know about, so that the mind is not

led to a conclusion about their constant and regular conjunction through anything it knows of their nature. All that past

experience can tell us, directly and for sure, concerns the behaviour of the particular objects we observed, at the

particular time when we observed them. {My experience directly and certainly informs me that that �re consumed

coal then; but it is silent about the behaviour of the same �re a few minutes later, and about other �res at any time.} Why

should this experience be extended to future times and to other objects, which for all we know may only seem similar? -

that is what I want to know. The bread which I formerly ate nourished me; that is, a body with such and such sensible

qualities did at that time have such and such secret powers. But does it follow that other bread must also nourish me at

other times, and that the same perceptible qualities must always be accompanied by the same secret powers? It does not

As you read, consider the following questions:

What would be an example of an “inference from experience”?

What is the difference between demonstrative and factual reasoning?

How do cause and effect relationships affect our knowledge of physical objects?

Why do we assume that the future will be like the past?

Making Connections

Hume’s use of logic and argument and propositions is very important, like the logic section in Unit 1. Relations of ideas are frequently found in deductive arguments based on de�nitions of terms. Matters of fact are often described as inductive since they feature predictions (“the sun will rise…”) and generalizations.

When Hume describes facts, he emphasizes things we have direct impressions of using our senses. Plato wants facts to be ideas and forms we experience through reason. Do we need some prior knowledge or familiarity to understand some sense information?

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seem to follow necessarily. Anyway, it must be admitted that in such a case as this the mind draws a conclusion; it takes a

certain step, goes through a process of thought or inference, which needs to be explained. These two propositions are far

from being the same:

I have found that such and such an object has always had such and such an effect.

I foresee that other objects which appear similar will have similar effects.

The second proposition is always inferred from the �rst; and if you wish I shall grant that it is rightly inferred. But if you

insist that the inference is made by a chain of reasoning, I challenge you to produce the reasoning. The connexion between

these propositions is not intuitive [that is, the second does not self-evidently and immediately follow from the �rst]. If the

inference is to be conducted through reason alone, it must be with help from some intermediate step. But when I try to

think what that intermediate step might be, I am defeated. Those who assert that it really exists and is the origin of all our

conclusions about matters of fact owe us an account of what it is.

{They have not given any account of this, which I take to be evidence that none can be given.} If many penetrating and able

philosophers try and fail to discover a connecting proposition or intermediate step through which the understanding can

perform this inference from past effects to future ones, my negative line of thought about this will eventually be found

entirely convincing. But as the question is still new, the reader may not trust his own abilities enough to conclude that

because he cannot �nd a certain argument it does not exist. In that case I need to tackle a harder task than I have so far

undertaken - namely, going through all the branches of human knowledge one by one, trying to show that none can give us

such an argument.

All reasonings fall into two kinds: (1) demonstrative reasoning, or that concerning relations of ideas, and (2) factual

reasoning, or that concerning matters of fact and existence. That no demonstrative arguments are involved in (2) seems

evident; since there is no outright contradiction in supposing that the course of nature will change so that an object which

seems like ones we have experienced will have different or contrary effects from theirs. May I not clearly and distinctly

conceive that snowy stuff falling from the clouds might taste salty or feel hot? Is there anything unintelligible about

supposing that all the trees will �ourish in December and lose their leaves in June? Now, if something is intelligible and

can be distinctly conceived, it implies no contradiction and can never be proved false by any demonstrative argument or

abstract a priori reasoning.

So if there are arguments to justify us in trusting past experience and making it the standard of our future judgment, these

arguments must be probable only; that is, they must be of the kind that concern matters of fact and real existence, to put

it in terms of the classi�cation I have given. But probable reasoning cannot provide us with the argument we are looking

for, if I have described it accurately. According to my account, all arguments about existence are based on the relation of

cause and effect; our knowledge of that relation is derived entirely from experience; and in drawing conclusions from

experience we assume that the future will be like the past. So if we try to prove this assumption by probable arguments,

i.e. arguments regarding existence, we shall obviously be going in a circle, taking for granted the very point that is in

question.

In reality, all arguments from experience are based on the similarities that we �nd among natural objects - which lead us

to expect that the effects of the objects will also be similar. Although only a fool or a madman would ever challenge the

authority of experience or reject it as a guide to human life, still perhaps a philosopher may be allowed to ask what it is

about human nature that gives this mighty authority to experience and leads us to pro�t from the similarities that nature

has established among different objects. Our inferences from experience all boil down to this: From causes which appear

similar we expect similar effects. If this were based upon reason, we could draw the conclusion as well after a single

instance as after a long course of experience. But that is not in fact how things stand. Nothing so like as eggs; yet no-one

expects them all to taste the same. When we become sure of what will result from a particular event, it is only because we

have experienced many events of that kind, all with the same effects. Now, where is that process of reasoning which infers

from one instance a conclusion that was not inferred from a hundred previous instances just like this single one? I ask this

for the sake of information as much as with the intention of raising dif�culties. I cannot �nd - I cannot imagine - any such

reasoning. But I am willing to learn, if anyone can teach me.

It may be said that from a number of uniform experiences we infer a connexion between the sensible qualities and the

secret powers; but this seems to raise the same dif�culty in different words. We still have to ask what process of

argument this inference is based on. Where is the intermediate step, the interposing ideas, which join propositions that

are so different from one another? It is agreed that the color, consistency and other sensible qualities of bread do not

appear to be inherently connected with the secret powers of nourishment and support. If they were, we could infer these

secret powers from a �rst encounter with those perceptible qualities, without the aid of long previous experience; and

this contradicts what all philosophers believe and contradicts plain matters of fact. Start by thinking of us in our natural

state of ignorance, in which we know nothing about the powers and in�uence of anything. How does experience cure this

ignorance? All it does is to show us that certain {similar} objects had similar effects; it teaches us that those particular

objects had such and such powers and forces at those particular times. When a new object with similar perceptible

qualities is produced, we expect similar powers and forces and look for a similar effect. We expect for instance that stuff

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with the color and consistency of bread will nourish us. But this surely is a movement of the mind which needs to be

explained. When a man says "I have found in all past instances such and such sensible qualities conjoined with such and

such secret powers", and then goes on to say "Similar sensible qualities will always be combined with similar secret

powers", he is not guilty of merely repeating himself; these propositions are in no way the same. The second proposition is

inferred from the �rst, you may say; but you must admit that the inference is not intuitive [that is, it cannot be seen at a

glance to be valid], and it is not demonstrative either [that is, it cannot be carried through by a series of steps each of

which can be seen at a glance to be valid]. What kind of inference is it, then? To call it experiential is to beg the question.

For all inferences from experience are based on the assumption that the future will resemble the past, and that similar

powers will be combined with similar sensible qualities. As soon as the suspicion is planted that the course of nature may

change, so that the past stops being a guide to the future, all experience becomes useless and cannot support any

inference or conclusion. So no arguments from experience can support this resemblance of the past to the future,

because all such arguments are based on the assumption of that resemblance. However regular the course of things has

been, that fact on its own does not prove that the future will also be regular. It is no use your claiming to have learned the

nature of bodies from your past experience. Their secret nature, and consequently all their effects and in�uence, may

change without any change in their perceptible qualities. This happens sometimes with regard to some objects: Why may

it not happen always with regard to all? What logic, what process of argument, secures you against this? You may say that I

do not behave as though I had doubts about this; but that would re�ect a misunderstanding of why I am raising these

questions. When I am considering how to act, I am quite satis�ed that the future will be like the past; but as a philosopher

with an inquiring - I will not say skeptical - turn of mind, I want to know what this con�dence is based upon. No reading or

enquiry has yet been able to remove my dif�culty. Can I do better than to put the dif�culty before the public, even though

I may not have much hope of being given a solution? In this way we shall at least be aware of our ignorance, even if we do

not increase our knowledge.

It would be inexcusably arrogant to conclude that because I have not discovered a certain argument it does not really

exist. Even if learned men down the centuries have searched for something without �nding it, perhaps it would still be

rash to conclude with con�dence that the subject must surpass human understanding. Even though we examine all the

sources of our knowledge and conclude that they are un�t for a given subject, we may still suspect that the list of sources

is not complete or our examination of them not accurate. With regard to our present subject, however, there are reasons

to think that my conclusion is certainly right and that I am not arrogant in thinking so.

It is certain that the most ignorant and stupid peasants, even infants, indeed even brute beasts, improve by experience

and learn the qualities of natural objects by observing their effects. When a child has felt pain from touching the �ame of a

candle, he will be careful not to put his hand near any candle, and will expect a similar effect from any cause which is

similar in its appearance. If you assert that the child's understanding comes to this conclusion through a process of

argument, it is fair for me to demand that you produce that argument, and you have no excuse for refusing to comply. You

cannot say that the argument has eluded you because it is so dif�cult and complex, because you have said that a mere

infant �nds it easy! So if you hesitate for a moment, or if after re�ection you produce any intricate or profound argument,

you have in effect given up your side in this dispute: you have as good as admitted that it is not reasoning which leads us

to suppose the future to resemble the past and to expect similar effects from apparently similar causes. This is the

proposition which I intended to establish in the present section. If I am right about it, I do not claim it as any great

discovery. If I am wrong, then there is an argument {from past to future} which was perfectly familiar to me long before I

was out of my cradle, yet now I cannot discover it. What a backward scholar I must be!

Hume on Induction

There are different ways to take Hume's argument. Hume did not regard himself as a skeptic, and he denied that his aim

was to undermine our con�dence in causation or induction. As he wrote elsewhere, he was primarily concerned to

discover the source of our beliefs and subject them to philosophical scrutiny. In a letter to a friend, Hume wrote:

But allow me to tell you, that I never asserted so absurd a Proposition as that any thing might arise without a Cause: I only

maintain'd, that our Certainty of the Falsehood of that Proposition proceeded neither from Intuition nor Demonstration; but

from another Source. That Caesar existed, that there is such an Island as Sicily; for these Propositions, I af�rm, we have no

demonstrative nor intuitive Proof. Would you infer that I deny their Truth, or even their Certainty? There are many different

kinds of Certainty; and some of them as satisfactory to the Mind, tho perhaps not so regular, as the demonstrative kind. 

--David Hume, from a letter dated by the editor February 1754. Taken from The Letters of David Hume, edited by J.

Y. T. Greig. Vol. I, p. 187, Letter 91.

Hume would certainly make the same claim about induction: he acknowledges that inductive arguments are "satisfactory

to the mind" — that is, we are quite settled and con�dent in accepting the conclusions of such arguments. Only a fool or a

madman, he says, could even imagine living without making inductive arguments. In fact, we may be more con�dent about

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inductive arguments than about deductive ones: some deductive arguments are complicated and long. After considering a

long mathematical proof, we might be quite uncertain about the result. Can we be sure that some error or false step did

not pass by unnoticed?

On the other hand, we are probably all quite con�dent that the sun really will rise tomorrow. Hume does not expect that

his argument will undermine our con�dence, but he does hope that an understanding of his argument will help us to be

more self-re�ective about the nature of this con�dence. If we cannot �nd fully rational justi�cation for even simple and

ordinary beliefs, then perhaps we should be more modest about the claims we make in ordinary life.

How is Hume's skepticism about induction related to the more general skepticism we saw in Descartes? Is Hume's

skepticism more radical, or less radical than Descartes'?

For more study and to check your knowledge, complete the Unit 3 Self Assessment - Hume (not graded).