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An Enquiry Concerning Human Understanding | Quotes


If we can go no farther than this mental geography ... it is at least a satisfaction to go so far.

David Hume, Section 1

Hume proposes an empirical approach to developing a science of the mind. He seeks a "delineation of the distinct parts and powers of the mind."


The most lively thought is still inferior to the dullest sensation.

David Hume, Section 2

Hume claims that ideas are copies of sense impressions. As copies, they can never have as much "force and vivacity" as the impressions.


When we [suspect] that a philosophical term is employed without any meaning ... we need but inquire, from what impression is that supposed idea derived?

David Hume, Section 2

Hume argues that all legitimate ideas are traceable back to a sense impression.


The contrary of every matter of fact is still possible; because it can never imply a contradiction.

David Hume, Section 3

Hume distinguishes experiential from purely rational reasoning. Conclusions according to the former mode of reasoning are always probable. They can never be certain, as is the case of logically correct (valid) reasoning.


Knowledge of [causation] ... arises entirely from experience, when we find, that any particular objects are constantly conjoined with each other.

David Hume, Section 3

Unlike rationalist philosophers such as Descartes, Hume rejects the claim that human rationality alone can determine causal relations.


The effect is totally different from the cause, and consequently can never be discovered in it.

David Hume, Section 3

A number of other thinkers claimed that causes contain their effects, so that by mere examination of a cause, one can find its effect. Hume rejects this view, arguing instead that the objects and events involved in causal sequences are entirely separate.


All our experimental conclusions proceed upon the supposition, that the future will be conformable to the past.

David Hume, Section 4

Hume points out that the problem in attempting to prove the legitimacy of causal reasoning is that the proof enlists the very reasoning it is trying to prove. Causal reasoning is the foundation of experiential reasoning. So experiential reasoning cannot be used to justify causal inferences. There is, however, no other justification available. This means that causation is not justified by rational means.


Custom, then, is the great guide of human life.

David Hume, Section 5

Hume's solution to the problem of causation's lack of rational or empirical justification is custom. One becomes accustomed to events occurring together, so one concludes that one event causes another.


Belief is nothing but a more vivid, lively, forcible, firm, steady conception of an object, than what the imagination alone is ever able to attain.

David Hume, Section 5

Hume distinguishes knowledge from belief. The former is derived from sense impressions, while the latter is a psychological state that emerges from certain types of experience.


When we [study] external objects, and consider the operation of causes, we are never able ... to discover any power or necessary connection ... which binds the effect to the cause.

David Hume, Section 7

Hume applies his conclusions about causation and its related idea, necessary connection, to the question of the existence of objects that are independent of the mind.


Cause [is] an object, followed by another, and where all the objects, similar to the first, are followed by objects similar to the second.

David Hume, Section 7

Here, Hume provides a definition of cause as a sequence of events that indicates a specific, necessary, relation. He continues, "If the first object had not been, the second never had existed."


The conjunction between motives and voluntary actions is as regular and uniform, as that between the cause and effect in ... nature.

David Hume, Section 8

Hume applies the definition of causation to the relation between human motives and "free" actions.


We must not, however, expect ... that all men, in the same circumstances, will always act precisely in the same manner.

David Hume, Section 8

As with those events whose causes are not known, differing human motivations may lead to a diversity of actions. Human actions, even in the same circumstances, may vary depending upon "the diversity of characters, prejudices, and opinions" of each person.


Animals, as well as men learn many things from experience, and infer, that the same events will always follow from the same causes.

David Hume, Section 9

Hume thinks the difference between human and nonhuman animals is one of degree, not kind. For example, there are plenty of similarities between humans and other animals, including the development of causal inferences.


If we take ... any volume; of divinity or school metaphysics ... let us ask, Does it contain any abstract reasoning concerning quantity or number [or] any experimental reasoning concerning matter of fact and existence?

David Hume, Section 12

This quote ends the book. And Hume does give the answer to these compelling questions. He says that if the answer is in the negative, then "Commit it then to the flames: For it can contain nothing but sophistry and illusion." This conclusion reflects Hume's commitment to restricting claims to what can be justified by mathematical or experiential reasoning.

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