An Enquiry Concerning Human Understanding Informative Summary (2006 eBook)


“An Enquiry Concerning Human Understanding” is a work of moral philosophy that takes a skeptical approach to the nature of knowledge and human reasoning. David Hume argues that all our knowledge of the world derives from experience, and that reason alone cannot tell us anything about the nature of reality. He examines the relationship between cause and effect, arguing that we infer a necessary connection between events from a repeated experience of their conjunction, not from any inherent power or force in the cause itself. This principle, Hume argues, applies to both the physical world and human actions, and undermines the foundations of common sense and even morality.

Hume also tackles the question of liberty and necessity, arguing that all our actions are determined by our motives and circumstances, and that there is no such thing as true freedom of the will. He then applies this principle to the idea of God and providence, arguing that we can never have reason to infer any attributes or actions of God beyond those we see manifested in the world. Hume concludes by exploring the limits of skepticism, arguing that excessive skepticism is ultimately useless and can only lead to paralysis. He advocates for a more “mitigated” skepticism, which involves humility and a focus on practical and common-sense matters rather than remote and speculative questions.

Key Findings:

  • Limits of Human Reason: Hume asserts that human reason is limited to experiencing the world and drawing inferences based on observed regularities, as opposed to a priori reasoning.
  • Causality and Custom: We infer causality from observed conjunction of events, not from an inherent power or force. Custom is the true foundation of our knowledge of cause and effect.
  • Liberty and Necessity: All actions are determined by motives and circumstances. True freedom of the will is an illusion.
  • Providence and Skepticism: We cannot infer anything about God’s attributes beyond what we observe in the world. Excessive skepticism leads to paralysis, while a more “mitigated” skepticism focuses on practical matters and acknowledges the limitations of human reason.


  1. Euclid’s geometry is not dependent on the existence of circles or triangles: It deals with the relations of ideas, which are independent of any real-world objects.
  2. The idea of God is derived from reflecting on our own minds: We amplify our qualities of goodness and wisdom to imagine a supremely intelligent being.
  3. A blind man cannot form a notion of colors: Ideas are dependent on corresponding impressions from the senses.
  4. The explosion of gunpowder or the attraction of a loadstone could not be discovered by reason alone: These are events that are only known through experience.
  5. The human mind cannot assign the ultimate cause of any natural phenomenon: Our knowledge is limited to reducing complex events to simpler, general principles like gravity or elasticity.
  6. The connection between sensible qualities and secret powers is unknown: We cannot know why bread nourishes us based on its color, weight, or taste alone.
  7. Even after experiencing cause and effect, our conclusions are not based on reasoning: We infer future events based on past experience, but the basis of this inference is not a chain of reasoning.
  8. Experience cannot prove the resemblance of the future to the past: All inferences from experience assume that the future will resemble the past, and so cannot be used to prove that resemblance without circularity.
  9. Animals also learn from experience and infer future events: This shows that inference is not based on reasoning, but on custom.
  10. Experimental reasoning in humans and animals is a type of instinct: We are not consciously aware of the mental processes involved in drawing inferences.
  11. Chance is a negative word: It does not represent any real force or power in nature.
  12. There is no idea of power or necessary connexion in single instances of cause and effect: We only observe sequence, not the force by which one event produces another.
  13. The union of soul and body is a mystery: We cannot understand how a spiritual substance can influence a material one.
  14. The command of the will over our ideas is limited and not fully understood: We are not conscious of the power by which our minds produce new thoughts.
  15. The idea of power is not derived from consciousness of power in ourselves: We are only conscious of the events themselves, not the power by which they are produced.
  16. The vulgar explain unusual events by appealing to invisible intelligent principles: Philosophers, however, recognize that even the most familiar events involve incomprehensible forces.
  17. The theory that God is the immediate cause of all events diminishes his power: It is more powerful to create a universe that can operate on its own than to constantly intervene in its workings.
  18. We cannot argue from an inferred cause to new effects: All inferences concerning God’s attributes must be based on observed effects, not on assumed causes.
  19. We cannot infer from the observed order of the universe to a more perfect scheme in the future: We are only justified in concluding that God possesses the attributes we see manifested in the world, not any additional ones.
  20. The belief in a divine Providence is useless: If God is only known by his effects, we cannot infer any new effects from him, and so cannot use that belief to guide our actions or predict future events.


  1. 2,000 years: The length of the debate concerning liberty and necessity in philosophy.
  2. 1,000 years: The age of man according to the biblical account in the Pentateuch.
  3. 100 instances: The number of experiments on one side required to produce a “doubtful expectation” when weighed against 50 experiments on the other side.
  4. 120 witnesses: The number who gave oath for the miracle of Mademoiselle le Franc.
  5. Three years: The length of time Queen Elizabeth is said to have governed England after her supposed death and resurrection.
  6. Three volumes: The size of the book “Recueil des Miracles de l’Abb(c) Paris.”
  7. 1,600: The year in which a supposed eight-day darkness over the whole earth is said to have occurred.


  1. Moral Philosophy: The branch of philosophy that deals with the nature of morality, ethics, and human behavior.
  2. Association of Ideas: The psychological principle that explains how ideas connect to each other in the mind through resemblance, contiguity, and cause and effect.
  3. Impressions: Our more vivid and lively perceptions, such as sensations, feelings, and emotions.
  4. Ideas: Our less vivid and lively perceptions, which are copies of our impressions.
  5. Scepticism: A philosophical attitude of doubt and uncertainty, especially concerning the possibility of attaining knowledge.
  6. Necessity: The concept of a necessary connection between cause and effect, arising from the constant conjunction of events.
  7. Liberty: The power of acting or not acting according to the determinations of the will.
  8. Custom: The principle that explains how repeated experiences create habits and expectations in our minds.
  9. Miracle: A violation of the laws of nature, often attributed to the intervention of a supernatural being.
  10. Providence: The belief that God governs the world and intervenes in its affairs, often with a view to rewarding virtue and punishing vice.


  1. The example of Adam: Hume uses the example of Adam, who, despite being endowed with perfect reasoning abilities, could not have known the effects of water or fire without experience.
  2. The story of the watch found on a desert island: Hume uses this example to show how we infer past events from present evidence, based on the assumption of a connection between cause and effect.
  3. The example of two billiard balls: Hume uses this example to demonstrate the arbitrary nature of cause and effect: if we consider the situation a priori, there is no reason to assume that one billiard ball will cause the other to move.
  4. The example of heat and flame: Hume uses this example to illustrate the power of custom: we expect heat to follow flame because we have always observed that conjunction.
  5. The example of a picture of an absent friend: Hume uses this example to demonstrate how resemblance can enliven our ideas.
  6. The ceremonies of the Roman Catholic religion: Hume uses these as an example of how the mind seeks to make religious concepts more tangible through sensory experiences.
  7. The example of the son of a dead friend: Hume uses this example to show how the principle of causation can operate in the mind to revive past memories.
  8. The example of a person suffering from the gout: Hume uses this example to show how even a well-reasoned argument for the ultimate goodness of the universe is ineffective in practice when faced with the immediate suffering of individuals.
  9. The example of Alexander the false prophet: Hume uses this example to illustrate how the tendency towards the miraculous can be exploited, especially in societies with low levels of education and knowledge.
  10. The example of the miracle attributed to Vespasian: Hume uses this well-documented story to show how even seemingly strong evidence for a miracle can be overwhelmed by the inherent improbability of such an event.

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