For this lecture read Hume’s An Enquiry Concerning Human Understanding, sections I-V.


DAVID HUME (1711-1776) was born in Edinburgh, Scotland.  His name was originally spelled Home, but Hume changed it because his English colleagues kept mispronouncing it.  Like Descartes, he originally planned to study law but came to a fascination with philosophy and devoted himself to it instead.  During his lifetime his works on philosophy were condemned both by professors as unintelligible and priests as heretically atheist, but his six volume History of England gained fame and was printed numerous times.

While Hume was called an atheist by friends and foes, he was critical of religion but silent about his own beliefs.  It is likely he was an agnostic, as he argued in various places that reason could neither prove nor disprove the religious beliefs of the world’s cultures.  Hume saw religion not as objectively true or false but as useful to a culture in a time and place, similar to the Utilitarianism of John Stuart Mill and the Functionalism of William James, the Pragmatist.  In Hume’s History of England, he argues that humans are creatures of habit who are often moved to political revolution only over matters of religion.  One could extend this to ideology in modern times, systems and cultures of belief and practice.  Over the course of English history, religion was often the only power other than the nobility that could put the monarchy in check.

Hume’s radically skeptical position, the one that awoke Kant from his “dogmatic slumbers”, as Kant later wrote after reading Hume, is that all of our thinking, our identity and beliefs are assumptions, habits, and prejudices, acquired through experience and induction.  This is similar to the Buddhist theory that the mind and all of its concepts, including identity and memories, are skandas, ‘piles’ that accumulate over time.  Buddhists often use this to illustrate the doctrine of impermanence, that all things are mortal and temporary.  Also like Buddhism, Hume argued that reason is ruled by the passions, not independent of them.  Hume had access to Buddhist views through Jesuit scholars and missionaries who had traveled to Thailand and Tibet, a theory put forward by Alison Gopnik, a developmental psychologist at UC Berkeley who argues that children are tiny scientists.  This would make Gopnik, as well as all of us, experienced Empiricists.


Hume’s text An Abstract of A Treatise of Human Nature is the condensed form of Hume’s first and foremost work, A Treatise of Human Nature, which he wrote after critics claimed the original was convoluted and difficult to understand.  Hume begins saying that philosophy has flowered all over Europe in “these last four score years” (80 years, no connection to Lincoln or Gettysburg), and that it has occurred in England just as greatly as any other.  Notice that philosophy for Hume is a recent development for Europe as well as England.

Hume says that philosophers of ancient times have handled their truths delicately, showing more restraint than full depth of reflection.  Remember that with Descartes, skepticism and critical reflection can quickly turn to dogmatism and orthodoxy.  Hume argues that all truth is assumption and habit, which means that any accepted truth must be continuously justified rather than simply proved once with reason, a position Foucault will argue about power.  This opens up the potential for continuous questioning of all established and institutionalized forms of knowledge.

Hume Perceptions, Impressions and Ideas

Hume says that all mental activities are perceptions, and that perceptions are divided into two kinds: impressions and ideas Impressions are perceptions of objects and others that are present, and ideas are perceptions of objects and others that are not present or not directly perceived.  For example, if we have the perception of a red billiard ball on the table, this is an impression.  If we turn away from the table such that we are no longer looking at the ball, we must imagine the billiard ball as an idea.  This is also a perception, something experienced, but the second perception, our imaginary idea, is caused by and derived from the first, our visual impression.

Hume used billiards, a leisure activity for aristocrats such as himself, to illustrate his criticism of our conceptions of causation.  Likewise, if one looks at the red ball as it is moving, one has an impression of the ball at each point in time, and must conceive of the motion as a whole in the mind with a concept, never perceiving it all at one time.  Hume argues that we derive all of our ideas from our impression, and that impressions are strong and direct, while ideas are weaker and indirect.  Hume acknowledges that this is in line with Locke’s idea of the mind as tabula rasa, that we are a blank slate upon which experience impresses its forms.  This goes directly against Descartes and Kant, who believe we can with the operation of reason determine truth independent of experience.

Hume presents us with his famous and central billiard ball analogy.  Imagine two billiard balls, one red and one blue, and that the red ball rolls down the table, strikes the blue ball, and causes it to move.  There are three events here.  First, the red ball moves up to the blue ball.  Second, there is the sound of a ‘clack’ as the two presumably collide.  Third, the blue ball moves away from the red ball.  Naturally, we acquire a habit of perception involving both impressions and ideas, and arrive at the understanding of causation, that the red ball struck the blue ball causing it to move.  We naturally assume that the motion of the red ball caused the motion of the blue ball.

boom comic

We must assume that A causes B because causation is an idea, not an impression, conceived in the mind, not perceived in the world.  We did not see the conjunction of the two events, but conceived of it.  While we saw two billiard balls meet, heard a ‘clack’ and then saw them part, none of these things characterize causation.  Causation is itself invisible.  It has no color, does not always involve motion nor does it always make a sound.  Since we are a blank slate, as Locke argued and Hume supports, Hume asks: How do we understand ball A caused ball B to move?  If causation involves various sets of sensations without a common factor, how can any particular impression lead to our idea?  If Hume was a Rationalist, he could claim that we reason that A caused B to move, but as an Empiricist, who, like Locke, argues that our ideas can always be wrong and experience can always present us with counterexamples, he makes a much more radical and skeptical claim.

The answer, Hume says, is that we have shared common experience, and so we share ideas and prejudices impressed upon us by our common experience.  Since we were babies, we have all seen solid things move into other solid things, followed by sounds and further movements.  While various sensations such as sights and sounds were involved, we each developed a similar idea of causation that we derived not from abstract reason but from direct experiences.  We developed a habit and prejudice such that when we watched the red ball moving toward the blue ball, we assumed that the blue ball would move, and then when our impression of the blue ball moving matched our idea, we assumed that our prediction was accurate and allowed it to further reinforce our idea.

Assumptions lead to and reinforce further assumptions, not certainties of reason leading to further certainties as the Rationalists would have it.  Our impressions of things knocking into each other, and in particular our impressions of billiard balls and their motions, naturally caused us all to have a preconception, a preconceived idea.  Feyerabend, skeptical philosopher of science, says that circular reason is not necessarily a fallacy, as it is the most dominant form of reasoning on the planet and much of the time it is perfectly correct.  Magicians report that when they pretend to throw a ball into the air but palm it instead, the adults in the audience see the ball rise up into the air and disappear, a shared hallucination that young children do not see, because the adults have been impressed so thoroughly by their shared experience.

Consider that we could make a movie of the two billiard balls, filming ball A striking ball B, and then display the film to an audience.  While every member of the audience would assume that ball A caused ball B to move, they are all watching an image, not the physical act, and so the image of ball A is not causing the image of ball B to move.  It is the media of the film, today digital data, that causes the image of ball B to appear and move.  It is an illusion that one image is striking the other.  Obviously, we want the audience of the film to have this idea, but this does not make it any less of an illusion, whether the billiard balls are filmed or animated.  In a sense, when we watch animation we know and don’t know that what is going on is ‘real’.  We can ‘suspend’ our disbelief, and allow our minds to watch and believe in the animated events, even though any animation must, by its nature, be false caricatures of events.


It is very similar to the Belgian Surrealist painter Magritte’s painting which reads, “This is not a pipe”, displaying the image of a pipe.  We can gaze at a painting of a pipe, know very well that this pipe cannot be used as a pipe, yet suspend our disbelief to accept the image as a representation that the painter is conveying to us.  Magritte’s painting is an attempt to invert this situation, an image that draws attention to being a mere representation rather than allow the spectator to ignore the fact.  Likewise, we can construct an animatronic billiard table, like at a ride in Disneyland, that looks like objects are hitting each other over and over again even if the sound is artificial and the objects never touch.  Barthes, the French philosopher and literary critic, said that now that we have built Disneyland, maybe we will be more critical of ideology.  Baudrillard, fellow French philosopher and pessimist, would disagree and argue that nothing in a society based on consumerism and mass advertising is anything other than image anymore.

While nothing can be known for certain, our impressions do accumulate and build up in our ideas, and thus they are real and useful to us.  They are not so real that they ensure that nothing could ever contradict them, but they are real to us and we often use them successfully in the world.  Hume uses the example of Adam in the garden of Eden as a human who learns by experience, starting with a blank slate, writing:

“Even Adam, with all his science, would never have been able to demonstrate that the course of nature must continue uniformly the same, and that the future must be conformable to the past.”

We are determined by custom alone to suppose the future conformable to the past.  When I see a billiard ball moving towards another, my mind is immediately carried by habit to the usual effect, and anticipates my sight by conceiving the second ball in motion… It is not, therefore, reason which is the guide of life, but custom.  That alone determines the mind, in all instances, to suppose the future conformable to the past.  However easy this step may seem, reason would never, to all eternity, be able to make it.

With regard to any matter of fact, however strong the proof may be from experience, I can always conceive the contrary, though I cannot always believe it… Philosophy would render us entirely Pyrrhonian were not nature too strong for it.

Hume argues that things are often variable and uncertain in life.  Using a modern example, very similar to examples used by Sextus Empiricus to support Pyrrhonian skepticism, Hume argues that thirty grains of opium will kill anyone that is not accustomed to it.  Clearly, Hume is accustomed to people using opium.

Hume questions the Cartesians’ idea of a supreme being which is wholly without deception, the eternal soul, and the absolute certainty of mathematical truths such as 2 + 3 = 5.  He argues that the Cartesians cannot know these things from experience, and they cannot derive them from reason.  Hume argued that the idea of God is a composition of our experience.  Human beings saw men with beards rule over things on high, and they project from their experiences in the world into realms unseen.  I have read a poll taken a few years ago that reported only 6% of Americans believe that God has a beard, though far more are monotheists.

proof that one equals two

Mathematical and geometric proofs look nice, but sometimes geometry seems like it is proving something that is later disproved, as Descartes himself notes as he imagines a demon that could deceive him even about forms of mathematics.  While Hume and other Empiricists would freely admit that it is very useful to follow one’s assumption that two and three always equal five, this is based on our experience of the durability of this truth in the world, not based on purely abstract reasoning.  There are even cases, such as the infamous proof that one equals two, which play on our regular use of mathematics that show its mechanics are not flawless.  If you figure out the trick to the proof, you will understand why additional rules are added to mathematics to correct the practice in cases that it breaks down.

As mentioned with Buddhism, Hume argued that emotion and reason are always intertwined, just as experience and reason are always intertwined.  He famously said, “Reason is, and ought only to be the slave of the passions”.  Without desire, we do not reason.  Recent literature about antidepressants suggests that when people are significantly devoid of desire, they do not find themselves thinking much, are not motivated to have significant ideas about important things.  When we think much about something, we are passionate.  If one tries to solve an argument between two parties without being biased either way, this is because one has a desire to solve the problem, not proof that one has no desires or concerns at all.  If one had no concerns at all, one would simply wander away from the problem.

Eight years after Hume published his Treatise on Human Nature (1740) and then his condensed Abstract of a Treatise on Human Nature (1740) to clarify and popularize his ideas, he composed his Enquiry Concerning Human Understanding (1748), to further simplify his ideas and argue for them more forcefully, which fits with his theory that it is passion, not pure reason, which drives meaning, understanding, and life.  It is this book which woke Kant from his “dogmatic slumbers”, which then lead to many other thinkers, including Hegel, Schopenhauer, Nietzsche and all these Germans influenced after Hume the lone Scotsman.

Hume begins by distinguishing between two species of philosophy, the active and the rational.  Hume is well aware of the difference between Rationalists such as Descartes and Leibniz, and Empiricists such as Locke, whom he uses but also dismisses, and himself.  The active philosopher pursues and avoids this and that in life to be good, using anything and everything from everyday life to explain things in an easy and obvious way, making us feel the difference between living wisely and foolishly.

The rational philosopher considers reason rather than action, and seeks truth rather than ways of living, narrowly examining human nature to find principles that regulate understanding, excite our feelings and judge this thing in that way.  Rational philosophers think it is a scandal that humanity hasn’t fixed the foundation of morality and reasoning yet beyond all controversy, but they talk forever without establishing these foundations.  Pushing from individual thing towards absolute universal principles and the proper bounds of justified, certain reason.

The average person finds rational philosophers abstract and unintelligible, and most people will always prefer philosophers of action, explaining things in easy, useful ways, than those who use complicated abstractions.  Rational philosophy vanishes when the rationalist leaves the shade and gets to any work, and rational principles cannot easily influence our behavior.  The feelings of the heart reduce the rational from profound to poor.  Active philosopher have acquired just, durable fame, while rational philosophers have acquired a “momentary reputation, from the caprice or ignorance of their own age”.  Hume doesn’t seem to like Rationalism, or academic philosophy, of Locke or anyone else, and Modern European philosophy is just getting started, as Hume himself says, over the hundred years just before Hume himself.  Hume says, “Locke will be entirely forgotten,” lumping Locke, his fellow Empiricist, firmly with the “rational” camp.

The philosopher is a character who supposedly does nothing for the world, wrapped up in reasonings beyond the comprehension of the public, but the public despises the fool even more than they suspect the wise of foolishness.  The balanced character engages with the public, the sciences and arts, while remaining also detached and apart, leading to the easy and useful active style and species of philosophizing, such that the student can be sent back to life with some ability and wisdom.

Humanity is reasonable being, but science can’t satisfy our need for meaning.  Humanity is a social being, but company and society cannot satisfy us entirely either.  Humanity is an active being, but we need relaxation as well.  All this suggests a mixed and balanced life is best, and we shouldn’t draw too much from one thing such that we can’t draw from another.  We should do science while keeping science human and humane, and thought which becomes too abstract is punished with depression, received coldly, and condemned to obscurity.  Be philosophical, but also be human.

“All polite letters are nothing but pictures of human life in various attitudes and situations; and inspire us with different sentiments, of praise or blame, admiration or ridicule, according to the qualities of the object, which they set before us.  An artist must be better qualified to succeed in this undertaking, who, besides a delicate taste and a quick apprehension, possesses an accurate knowledge of the internal fabric, the operations of the understanding, the workings of the passions, and the various species of sentiment which discriminate vice and virtue.  How painful this inward search or enquiry may appear, it becomes, in measure, requisite to those, who would describe with success the obvious and outward appearances of life and manners.  The anatomist presents to the eye the most hideous and disagreeable objects; but his science is useful to the painter in delineating even a Venus or a Helen.”

Hume says that much philosophy has been concerned with proving the existence of God.  While much effort is made to refute atheism and skepticism, it is also asserted that complete atheism and skepticism are impossible.  Hume wonders how a knight could continuously wander the countryside, seeking to defeat dragons and giants, while convinced that they do not exist.  I must say as a skeptical person myself, I have found it continuously amusing to hear again and again that skepticism is a problem that must be overcome, in spite of the fact that skepticism remains, apparently, as yet undefeated.  Sextus, the Pyrrhonian, argued that because dogmatists argue against skepticism as well as each other, they betray their own position and give us good evidence that their dogmas can be doubted and opposed.

straw bent in water

Hume criticizes Descartes and the Rationalists who seek an absolute and unquestionable starting point from which to reason.  Such a point does not exist as all truth can be doubted, which ancient Pyrrhonian skepticism recommended.  If each and every sensation can be doubted, then so can each and every act of reasoning.  While the Pyrrhonians such as Sextus used examples such as an oar appearing bent in water, Hume is concerned that Descartes can doubt sensation as well as any Pyrrhonian but cannot doubt reason, and attempts to defeat Pyrrhonian skepticism through the use of reason.  It seems that conception is more difficult to doubt than perception.  For Hume, this is disturbing, given that all of our reasoning and ideas are derived from and dependent on sensation.

Hume argues that the great subverter of skepticism is employment, the occupations of common life.  Because we must act and eat, we cannot afford to be entirely skeptical.  While it is easier to be skeptical in a school or in the shade, as soon as we are passionate about things in the world, skepticism, even for the hardened and determined skeptic, vanishes like smoke.  The only genuine profession for the skeptic is philosophy.  If the entire world were made of nothing but skeptical philosophers, humanity would die out, but thankfully we are naturally ignorant, passionate, and dogmatic, and so skepticism is continuously useful for showing most people the continuous errors of their ways and that for every position there is a counter position even if it does not seem apparent at first.  Thus, while skepticism, philosophy and doubt would be worthless if they eclipsed all dogmatism, vocation and belief, they are the most useful of positions and vocations, in critical opposition to everything else on Earth.