An Enquiry Concerning Human Understanding

It is only experience, which teaches us the nature and bounds of cause and effect, and enables us to infer the existence of one object from that of another. Such is the foundation of moral reasoning, which forms the greater part of human knowledge, and is the source of all human action and behaviour.

It is universally allowed by modern enquirers, that all the sensible qualities of objects, such as hard, soft, hot, cold, white, black, etc are merely secondary, and exist not in the objects themselves, but are perceptions of the mind, without any external archetype or model, which they represent. If this be allowed, with regard to secondary qualities, it must also follow with regard to the supposed primary qualities of extension and solidity; nor can the latter be any more entitled to that denomination than the former. The idea of extension is entirely acquired from the senses of sight and feeling; and if all the qualities, perceived by the senses, be in the mind, not in the object, the same conclusion must reach the idea of extension which is wholly dependent on the sensible ideas or the ideas of secondary qualities. Nothing can save us from this conclusion, but the asserting, that the ideas of those primary qualities are attained by Abstraction, an opinion, which, if we examine it accurately, we shall find to be unintelligible, and even absurd. An extension, that is neither tangible nor visible, cannot possibly be conceived: and a tangible or visible extension, which is neither hard nor soft, black nor white, is equally beyond the reach of human conception.

Bereave matter of all its intelligible qualities, both primary and secondary, you in a manner annihilate it, and leave only a certain unknown, inexplicable something, as the cause of our perceptions; a notion so imperfect, that no sceptic will think it worthwhile to contend against it.

If a tree falls in the middle of a forest, does it make a sound? - George Berkeley

Hume's classic philosphical investigation into the nature and limits of human knowledge and its acquisition.

p. 2 If they can discover

p. 2 If they can discover some hidden truths which may contribute to the instruction of posterity.
p. 5 defines metaphysics as the "absolute rejection of all profound reasonings
p. 6 of any art or profession: "a spirit of accuracy carries all of them nearer their perfection, renders them more subservient to the interests of society"
p. 8 the mind is endowed with several powers and faculties, that these powers are distinct from each other, that what is really distinct to the immediate perception may be distinguished by reflexion: and consequently, that there is a truth and falsehood, which lie not beyond the compass of human understanding. There are many obvious distinctions of this kind, such as those between the will and understanding, the imagination and passions, which fall within the comprehension of every human creature; and the finer and more philosophical distinctions are no less real and certain, though more difficult to be comprehended.

p. 13 the less forcible and lively are commonly denominated Thoughts or Ideas--- impression- all our more lively perceptions, when we hear, or see, or feel, or love, or hate, or desire, or will. And impressions are distinguished from ideas, which are less lively perceptions, of which we are conscious, when we reflect on any of those sensations or movements above mentioned.
p. 13-14 creative power of the mind amounts to no more than the faculty compounding, transposing, augmenting, or diminishing the materials afforded us by the sense and experience.
p. 16 When we entertain, therefore, any suspicion that a philosophical term is employed without any meaning or idea (as is but too frequent), we need but enquire, from what impression is that supposed idea derived? And if it be impossible to assign any, this will serve to confirm our suspicion."

p. 18 But that this enumeration is complete and that there are no other principles of association except these, may be difficult to prove to the satisfaction of the reader, or even to a man's own satisfaction. All we can do, in such cases, is to run over several instances, and examine carefully the principle which binds the different thoughts to each other, never stopping till we render the principal as general as possible

Propositions of this type are discoverable by the mere operation of thoughts, without dependence on what is anywhere existent in the universe

p. 20 All reasonings concerning matter of fact seem to be founded on the relation of cause and effect- near or remote, direct or collateral

p. 20 causes and effects are discoverable, not by reason but by experience

p. 24 the utmost effect of human reason is to reduce the principles, productive of natural phenomena, to a greater simplicity, and to resolve the many particular effects into a few general causes, by means of reasonings from analogy, experience and observation

p. 36 Reason is incapable of such variation. The conclusions which it draws from considering one circle are the same which it would form upon surveying all the circles in the universe.
All inferences from experience are effects of custom, not of reasoning.

p. 39 nothing but a more vivid, lively, forcible, firm, steady conception of an object, than what the imagination alone is ever able to attain
p. 41 customary conjunction of the object with something present ot the memory or senses
p. 42 Sensible objects have always a greater influence on the fancy than any other; and this influence they readily convey to those ideas to they are related, and which they resemble.

p. 47 There are some causes, which are entirely uniform and constant in producing a particular effect; and no instance has ever yet been found of any failure or irregularity in their operation... but there are other causes which have been found more irregular and uncertain
p. 48 Though we give the preference to that which has been found most usual, and believe that this effect will exist, we must not overlook the other effects, we must not overlook the other effects, but must assign to each of them a particular weight and authority, in proposition as we have found it to be more or less frequent.

p. 50 There are no ideas, which occur in metaphysics, more obscure and uncertain than those of power, force, energy or necessary connexion, of which it is every moment necessary for us to treat in all our disquisitions.
p. 51 all our ideas are nothing but copies of our impressions, or, in other words, that it is impossible for us to think of anything, which we have not antecedntly felt, either by our external or internal senses
p. 52 external objects are they appear to the sense, give us no idea of power or necessary connexion
p. 62 one object connected with another -- they have acquired a connexion in our thought and give rise to this influence, by which they become proof of each other's existence

p. 66 the economy of the intellectual system or region of spirits
p. 67 Beyond the constant conjunction of similar objects, and the consequent influence from one to the other, we have no notion of any necessity or connexion
p. 74 It seems almost impossible, therefore, to engage either in science or action of any kind without acknowledging the doctrine of necessity, and this inference from motive to voluntary actions, from characters to conduct.
p. 76 particular objects are constantly conjoined together, and that the mind is carried, by a customary transition, from the appearnce of one to the belief of the other.
p. 78 By liberty... we can only mean a power of acting or not acting, according to the determinations of the will
p. 79 There is no method of reasoning more common, and yet none more blameable, than in philosophical disputes, to endeavor the refutation of any hypothesis, by a pretence of its dangerous consequences to religion or morality.