An Enquiry Concerning Human Understanding by David Hume

Hume is considered one of the greatest modern philosophers and perhaps the greatest English philosopher to have ever written. Hume’s work deals with the way we learn (epistemology) and metaphysics. Many of his ideas overlap with psychology as well. Consider the following quote, which has many similarities to the idea of confirmation bias:

“Passion for philosophy, like that for religion, seems liable to this inconvenience, that, though it aims at the correction of our manners, and extirpation of our vices, it may only serve, by imprudent management, to foster a predominant inclination, and push the mind, with more determined resolution, towards that side which already draws too much, by the bias and propensity of the natural temper.”

In theory, philosophy possesses the potential to change us and challenge our most deeply-held assumptions, our sacred cows. Such a conception of philosophy is best illustrated by Socrates going out to the agora and challenging the knowledge of supposed experts on abstractions like beauty, piety, justice, etc. and showing these authorities that they are actually quite ignorant about these concepts.  In practice, however, philosophy often just confirms our natural inclinations, biases, and predispositions rather than challenging them. Hume attempts to show that much of what passes for philosophy, with the supposed purpose of clarifying our knowledge, actually only muddles our knowledge and when examined with a critical eye is really just sophistry. His main target is a certain type of metaphysics.

Like John Locke, he proposes an empirical theory of knowledge; basically, empiricism is the belief that we learn from our senses interacting with an outside external world. According to Hume, all our ideas derive from sensory impressions, with the exception of certain mathematical ideas, which can be derived from reason and abstract thinking. To challenge this proposition that thoughts are the products of the senses interacting with an external world, you might claim there is no such thing as a unicorn or a centaur, so where did those ideas come from? Hume would respond that even imaginative ideas are amalgamations of simpler impressions that ultimately have their origin in the external world. An imaginative creature like a unicorn is a just mixture of things that really do exist such as a horse and a horn (a concept we might have gotten from seeing a rhino, for example). A centaur is a combination of a horse and man, two simpler ideas that do exist in the real world. If you think of any imaginative idea you will find its constituent parts will stem from some real world sensory impression. Even the products of our deepest imagination comes from experience.

If we think about the flows of ideas in our head we will notice a logical connection between one idea and another. Hume claims there are three ways we connect ideas: resemblance, contiguity in time, and cause and effect.

  1. Resemblance: A painting of a pear would be an example of a resemblance; we understand it’s not a real pear, but paint on canvas assembled to recall the likeness of a pear.
  2. Contiguity: suppose we look at our apartment, we might begin to wonder what the apartment next to ours might look like. This would be an example of contiguity.
  3. Cause and effect: one event becomes associated with another event, such as a wound that makes us consider the pain that will follow.


Hume’s major contribution is the idea that cause and effect, which undergirds most of human knowledge, is not determined a priori or rationally, but arrives to us through experience. We see fire and then we experience heat following the lighting of the fire. The uniformity and consistency of this experience, the constant conjunction between these two as Hume would put it, leads us to infer that fire causes heat. This has important consequences. A rationalist account of cause and effect would suggest that we could look at an object, such as fire, and deduce using reason (just our thought process) what its effect might be. Hume is challenging this idea. In his account a person wouldn’t be able to just look at a fire and predict it will produce heat. It is only through experience that we come to know that fire causes heat. Not just one experience, but many repeated experiences cement this belief in our brain, which he calls custom and habit. It is also custom that makes us believe falsely that we can know causes and effects a priori through our reason alone, but Hume contends that you can’t guess an effect of the fire or any other object a priori (before anything happens), but are always basing your initial hypothesis on past experience. This means if we found an object new to us we wouldn’t be able to determine its cause or effects.  If a random stranger were born with a high IQ and the utmost level of reason such that his critical thinking and reasoning skills were somehow at the highest level possible if such a thing could be measured, and he was suddenly thrown into the world with no prior experiences of it whatsoever, Hume believes such a person wouldn’t be able to make any sense of the world, except as a series of random unconnected impressions, let alone have any conception of cause and effect relationships between various sensations.

Even though experience teaches us cause and effect relationship, we cannot use reason to understand the deeper reality behind it. We eat bread and we become nourished, but according to Hume we cannot know why the bread nourishes us. This is an important point. Hume is saying our mind is structured to identify cause and effect from the sensations of reality, but that we have no method of determining the reality behind the constant conjunction of events, therefore we have no way of knowing what causes “cause and effect.” Our inferences (Event A happens, then event B) aren’t rationally justified.


“experience only teaches us, how one event constantly follows another; without instructing us in the secret connexion, which binds them together, and renders them inseperable.”


When we notice cause and effect relationships they are not based on demonstrative proofs like a math problem, but rather on probability. Long periods of uniform experience increases our confidence in the results repeating. Different positions have different probabilities that increase or decrease over time so we assent to the position that has the best odds. We proceed into the future with the assumptions that the cause and effect relationships we have experienced will imitate what we have experienced in the past, even though we can’t actually be certain that they will. As he points out not all conjoined events happen together 100 percent of the time.

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

Wise people use experience as their guide and when many experiments show variability (sometimes this happens, but sometimes this other thing occurs instead), a wise man will side with what has the most likely probability.

He applies this same reasoning to the human psyche. We recognize from experience that the mind controls the body, but we can’t discern using reason how it is able to do so. Hume believes his theory can be applied to human action: motive and action in human behavior are the equivalent of cause and effect. If we can determine a motive of a person in question, then we can use our experience to determine with a high probability the action a person will perform. He accepts that this has limitations as there are many variables to human behavior that might make one human act one way in a situation and a different human act another way, but he does believe that there are certain predictions and expectations we can make about human behavior based on experience. We see then that this is not just a metaphysical and epistemological theory, but a psychological one as well. Like humans, Hume believes animals also learn from experience and infer “that the same events will always follow from the same causes.”

With this background, Hume attempts to address the problem of freewill versus determinism, which he identifies with the concepts of liberty and necessity. He argues that philosophical debate over the concepts of liberty and necessity stems from ambiguity of the terms and if we had better definitions all people would agree on the subject. This argument was a bit tricky to understand and I’m not sure I quite comprehended it perfectly myself. Necessity relates to cause and effect/motive and action. Liberty is the power of acting or not acting according to the determinations of the will. My liberty is my ability to choose between choices, such as moving my foot forward or keeping it in the same spot, depending on the dictate of my will (basically my whims or my mood at that moment). Now let’s look at another example and add necessity into the equation. Suppose after much soul-searching I come to realize that I desire to make lots of money (the determination of my will), my liberty allows me to pick between choices such as investing or getting a high-paying job to make lots of money (also I could’ve decided that I didn’t want to make lots of money and was happy with a medium amount), while necessity suggests my motive of greed will create predictable actions such as investing or getting a high-paying job. We can predict based on my motives what my actions will be and in that sense I’m determined or my actions are necessary. So his argument seems to be that we’re free to make our own choices based on our will, but once we do, we can use our experiences of human behavior to predict motive and action since human behavior has a certain regularity. The cause and effect relationship between motive and a person’s actions make my behavior predictable and necessary. Therefore Liberty should is not opposed to necessity; we have choices, but once we make a choice our motives and actions are necessary and predictable. Liberty’s true opposite then is constraint.

Hume also tackles religious ideas like G-d, miracles, and religious revelations. We can only know what experience is capable of teaching us. If men spend time talking about things they can’t ever get definitive knowledge about like the afterlife or the origin of worlds they will never reach a definitive conclusion due to the nature of these topics and therefore it is a waste of time and beyond the scope of human reason. Hume is suggesting that these ideas are the product of human imagination, faith, and revelation, not a proper domain for serious philosophical inquiry. Hume defines miracles as a violation of the laws of nature as it flies in the face of our everyday experience.

“There must, therefore, be a uniform experience against every miraculous event, otherwise the event would not merit that appellation. And as a uniform experience amounts to a proof, there is here a direct and full proof, from the nature of the fact, against the existence of any miracle.”

He is saying a miracle can only be called a miracle if it flies in the face of uniform experience. Since it flies in the face of uniform experience it is proof that miracles don’t exist. Therefore miracles don’t exist because they fly in the face of everyday experience. This seems like blatant circular reasoning. After all, if we agreed with his definition of miracle it would follow that if miracles did happen it wouldn’t be an everyday experience, but an event that happens extremely rarely.

He goes onto to grant a hypothetical argument in which G-d creates the universe (cause), but notes that even in such a situation we could not infer an afterlife exists because we can only infer from experience (none of us have experienced an afterlife and nothing about this world provides evidence of an afterlife). Any description of an afterlife must then be supposition or the product of imagination. He then tackles divine justice; if justice can be found in this world then there is no need for justice in an afterlife, and consequently there is no need to assume an afterlife exists. If there is no justice in this world, then the deity who is the creator of all things, is to blame, according to Hume. This seems a false dichotomy. There could be a mixture (some justice in this world, some in an afterlife), there could be other reasons why there is no justice in this world (such as Augustine’s concept of Original Sin), etc. It’s not like justice need be absolute or nonexistent altogether. Nevertheless, the bigger picture here is how experience should be our guide in our philosophical musings and to show how these type of philosophical questions aren’t grounded in experience.

All if this might seem a tangent to his main point about the nature of cause and effect, but it actually addresses the main goal of the work that he outlines in the beginning of his essay in which he is targeting a certain type of metaphysics. One might say his entire project is to outline an epistemology to reveal what kind of philosophical inquiries are permissible and what kind is just nonsense. So Hume includes these other philosophical questions to show that philosophical speculation about the afterlife, G-d, and such are the sorts of philosophical questions Hume believes is beyond the scope of human reason when it’s grounded in his observations about experience. In other words, these are the metaphysical speculations that he is taking to task in the beginning of the work and now he is looking at them more closely once he has shared his observations about how knowledge works.

“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 or existence? No. Commit it then to the flames: for it can contain nothing but sophistry and illusion.”

This is how Hume ends his work. The only knowledge we are capable of achieving through our reason is mathematics or that which we can ascertain through repeatable experiments relying on our senses, by which he means experience. Everything is just hot air.


3 thoughts on “An Enquiry Concerning Human Understanding by David Hume

    • Thanks. It’s tricky to summarize the ideas of philosopher in around 2000 words.

      Hume is definitely interesting and he has the advantage of writing in English, so you don’t have to worry about the accuracy of translation. I am working on reading Kant right now, which is a completely different experience!

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