principles which he enunciated in the Treatise of Human Nature were not essentially changed in any of his subsequent writings. In an advertisement to the authoritative edition of his Essays and Treatises, published in 1777, the year after his death, he says that henceforth he desired that his later writings alone should be regarded as containing his philosophical sentiments and principles; and it is only fair to concede that the original Treatise of Human Nature, which he composed at an early period of his life, did not in all points truly represent his later sentiments; yet it is mainly in the improvement, the ease and polish of his style, and in the omission of two parts of the original treatise, containing some of his most acute speculations, that his later writings differ from his earliest-a difference of form and finish rather than of thought and matter. Moreover, it is in the original treatise that Hume can be historically studied to the best advantage.

Although Hume's mind was original and vigorous, and his thinking and critical powers unusually great, yet he found the principles upon which he most effectively operated mainly in Locke and in Berkeley. There is little trace of the influence of Descartes in the Treatise of Human Nature; but his style bears internal evidence of the influence of French literature. No English philosophical writer of a prior date approached Hume in the qualities and the grace of his style.

On various points treated in the moral part of the treatise, the influence of Hobbes and of Hutcheson are easily traced; and Hume held the latter philosopher in very great esteem. Let us proceed to the exposition of his system, beginning with his own account of the state of his mind when he approached the subject:

"At the time therefore that I am tired with amusement and company, and have indulged a reverie in my chamber, or in a solitary walk by a river side, I feel my mind all collected within itself, and am naturally inclined to carry my view into all those subjects, about which I have met with so many disputes in the course of my reading and conversation, I cannot forbear having a curiosity to be acquainted with the principles of moral good and evil, the nature and foundation of government, and the cause of those several passions and inclinations which actuate and govern me. I am uneasy to think I approve of one object and disapprove of another; call one thing beautiful and another deformed; decide concerning truth and falsehood, reason and folly, without knowing upon what principles I proceed. I am concerned for the condition of the learned world,

which lies under such a deplorable ignorance in all these particulars. I feel an ambition to arise in me of contributing to the instruction of mankind, and of acquiring a name by my inventions and discoveries. These sentiments spring up naturally in my present disposition, and should I endeavour to banish them, by attaching myself to any other business or diversion, I feel I should be a loser in point of pleasure; and this is the origin of my philosophy." 3

He begins his exposition of the Understanding with a description of impressions and ideas, and resolves the perceptions of the mind into these two terms. The perceptions which enter the mind with most force he calls impressions, and this term includes all our sensations, passions, and emotions; by ideas he means the faint images of impressions excited in thinking and in reasoning. Having distinguished impressions and ideas into simple and complex classes, he then proceeds to discuss their qualities and relations. Impressions and ideas differ from each other only in the degrees of their vivacity -the one seems to be the reflection of the others; in the case, however, of complex ideas, he notices some exceptions to this doctrine; but seeing that all simple perceptions and ideas are copies of impressions, and that the complex ones are formed from them, therefore these two kinds of perceptions exactly correspond. He next starts the main subject the existence of impressions and ideas—and proposes to inquire which of them are causes and which effects.

He concludes that simple impressions are prior to their corresponding ideas, and that impressions are of two kinds-those of sensation and those of reflection. The first kind arise originally in the mind from unknown causes; the second are derived mostly from our ideas. Thus "An impression first strikes upon the senses, and makes us perceive heat or cold, thirst or hunger, pleasure or pain, of some kind or other. Of this impression there is a copy taken by the mind, which remains after the impression ceases, and this we call an idea. This idea of pleasure or pain, when it returns upon the soul, produces the new impressions of desire and aversion, hope and fear, which may properly be called impressions of reflection, because derived from it. These are again copied by the memory and imagination, and become ideas, which, perhaps, in their turn give rise to other impressions and ideas." At this stage he expresses his opinion

3 Book I., Part IV., sect. 7.

This is nearly the same as Hobbes' doctrine.

that the examination of the sensations belongs more to the anatomists and natural philosophers than to mental science, and therefore he does not enter upon them.5

Memory and imagination he treats together, but neither of them at much length. The first, he says, retains a strong and vivid impression, the second only a much fainter one. The chief distinction between memory and imagination consists in the fact that the memory retains the impressions in the order and form in which it receives them, while the imagination is not at all restricted in this way, as its function is to transpose and change its ideas. This power of the imagination he connects with his exposition of the association of ideas.

6

Ideas are associated in three ways-namely, by semblance, contiguity, and cause and effect. These relations are briefly explained as principles of association, with the remark that, of the three, the associative relations of causation are the most widely ramified. Among the effects of the association of ideas, the most remarkable are those complex ideas which are the common subjects of our thoughts and reasonings, and generally arise from some principle of union among our simple ideas. These complex ideas he divides into relations, modes, and substances; and proceeds to examine these.7

He classifies relations under seven general heads-(1) resemblance, the most essential requisite of philosophical relation; (2) identity; (3) space and time; (4) quantity or number; (5) objects having the same quantity, but in different degrees; (6) contrariety; and (7) cause and effect. He affirms that we have no idea of substance, except as a mere collection of particular qualities, and closes the first part of his treatise with a discussion of abstract ideas. He alludes

5 Book I., sects. 1, 2.

Further on he says "Nothing is more dangerous to reason than the flights of imagination. Men of bright fancies may in this respect be compared to those angels whom the Scriptures represent as covering their eyes with their wings."-Book IV., sect. 7. Again, in his later work, An Inquiry concerning Human Understanding, he remarks-"Nothing is more free than the imagination of man; and though it cannot exceed the original stock of ideas furnished by the external and internal senses, it has unlimited power of mixing, compounding, separating, and dividing these ideas, in all the varieties of fiction and vision."-Sect. 5, Part II.

7 Book I., Part I., sects. 3, 4. What he states above, however, should be compared with his treatment of the principles of association in his later work, An Inquiry concerning Human Understanding, sect. 3.

to Berkeley's view, and argues that abstract or general ideas are formed from individual and particular ones, and brings in the convenient term Custom, of which he makes so much use in his speculations "If ideas be particular in their nature, and at the same time finite in their number, it is only by custom they can become general in their representation, and contain an infinite number of other ideas under them."8

The second part of the Understanding contains a long and exceedingly penetrating discussion of the ideas of space and time. He opens with a few sentences of polished banter about the dispositions of philosophers and their disciples. The first serious point taken up is the doctrine of infinite divisibility, which is handled with consummate skill. Founding upon the limited power of the human mind, he proceeds vigorously to demolish it; and in the fourth section he puts it in this form :- “Our system concerning space and time consists of two parts, which are intimately connected together. The capacity of the mind is not infinite, consequently no idea of extension or duration consists of an infinite number of parts or inferior ideas, but of a finite number, and these simple and indivisible: it is, therefore, possible for space and time to exist conformable to this idea; and if it be possible, it is certain they actually do exist conformable to it, since their infinite divisibility is utterly impossible and contradictory.

"The other part of our system is a consequence of this. The parts, into which the ideas of space and time resolve themselves, become at last indivisible; and these indivisible parts, being nothing in themselves, are inconceivable when not filled with something real and existent. The ideas of space and time are, therefore, no separate or distinct ideas, but merely those of the manner or order in which objects exist; or, in other words, it is impossible to conceive a vacuum and extension without matter, or a time when there was no succession or change in any real existence." 9

The discussion is carried on through other three sections with great animation and ingenuity, and culminates in the annunciation of absolute Idealism, thus:-" Now since nothing is ever present to the mind but perceptions, and since all ideas are derived from something antecedently present to the mind, it follows that it is impossible for us so much as to conceive or form an idea of anything speci

8 Book I., Part I., sects. 5, 6, 7.

fically different from ideas and impressions. Let us fix our attention out of ourselves as much as possible; let us chase our imagination to the heavens, or to the utmost limits of the universe-we never really advance a step beyond ourselves, nor can we conceive any kind of existence, but those perceptions which have appeared in that narrow compass. This is the universe of the imagination, nor have we any idea but what is there produced." 10

The third part of the Understanding, which treats of knowledge and probability, is the longest in the book; many topics of great interest are handled in it; but I shall chiefly direct attention to his views on causation.

Knowledge and science mainly turn and rest on the various kinds of philosophical relation. He re-states the relations which have been already noticed in a preceding page, and expiscates them at length in his own manner. In treating causation, he begins by proposing to search for the origin of the idea; and finds it to be some relation among objects. He then seeks to discover what the relation itself is; but all that he discovers is that the two relations of contiguity and priority in time are essential to causation. But seeing that any object may be contiguous and prior to another without being considered as its cause, there is a necessary connection to be taken into account, and it is upon this, the most essential relation of causation, that he made his grand attack. It would be tedious to follow him through his long discussion, and in fact it is unnecessary; therefore, I will only indicate the lines of his method of investigating the subject, and its results.

He inquires why a cause is always necessary, and affirms that the real state of the question is "whether every object which begins to exist, must owe its existence to a cause; and this he continues, I assert neither to be intuitively nor demonstratively certain." After a very long exposition of the manner in which we reason beyond our immediate impressions, and conclude that particular causes must have particular effects, he takes up the discussion of the idea of necessary connection, and asks-"What is our idea of necessity, when we say that two objects are necessarily connected together? Upon this head I repeat what I have often had occasion to observe, that as we have no idea that is not derived from an impression, we must find some impression that gives rise to this idea of necessity, if

Book I., Part II., sects. 1, 2, 3, 4.

10 Book I., Part II., sects. 4, 5, 6.