we conceive. Something perfectly analogous to this may be remarked in the perceptions we obtain by the fense of fight. When I look into a fhew-box, where the deception is imperfect, I fee only a fet of paltry dawbings of a few inches diameter; but, if the representation be executed with fo much fkill, as to convey to me the idea of a diftant profpect, every object before me fwells in its dimenfions, in proportion to the extent of space which I conceive it to occupy; and what feemed before to be fhut up within the limits of a small wooden frame, is magnified, in my apprehenfion, to an immenfe landscape of woods, rivers, and mountains.

The phenomena which we have hitherto explained, take place when fleep feems to be complete; that is, when the mind lofes its influence over all those powers whose exercise depends on its will. There are, however, many cafes in which fleep feems to be partial; that is, when the mind lofes its influence over fome powers, and retains it over others. In the case of the fomnambuli, it retains its power over the limbs, but it poffeffes no influence over its own thoughts, and fcarcely any over the body; excepting those particular members. of it which are employed in walking. In madness, the power of the will over the body remains undiminished, while its influence in regulating the train of thought is in a great measure fufpended; either in confequence of a particular idea, which engroffes the attention, to the exclusion of every thing else, and which we find it impoffible to banish by our efforts; or in confequence of our thoughts fucceeding each other with fuch rapidity, that we are unable to stop the train. In both

of

of these kinds of madness, it is worthy of remark, that the conceptions or imaginations of the mind becoming independent of our will, they are apt to be mistaken for actual perceptions, and to affect us the fame in

manner.

By means of this fuppofition of a partial fleep, any apparent exceptions which the hiftory of dreams may afford to the general principles already stated, admit of an eafy explanation.

Upon reviewing the foregoing obfervations, it does not occur to me, that I have in any inftance tranfgreffed those rules of philofophifing, which, fince the time of Newton, are commonly appealed to, as the tests of found investigation. For, in the first place, I have not fuppofed any causes which are not known to exift; and fecondly, I have fhewn, that the phenomena under our confideration are neceffary confequences of the causes to which I have referred them. I have not fuppofed, that the mind acquires in fleep, any new faculty of which we are not conscious while awake; but only (what we know to be a fact) that it retains fome of its powers, while the exercise of others is fufpended and I have deduced fynthetically, the known phenomena of dreaming, from the operation of a particular class of our faculties, unconnected by the operation of another. I flatter myself, therefore, that this inquiry will not only throw fome light on the state of the mind in fleep; but that it will have a tendency to illustrate the mutual adaptation and fubferviency which exifts among the different parts of our conftitution, when we are in complete poffeffion of all the faculties and principles which belong to our nature *.

See Note [O].

CHAPTER FIFTH.

PART SECOND.

Of the Influence of Affociation on the Intellectual and on the Active Powers.

SECTION I.

Of the Influence of cafual Associations on our speculative

Conclufions.

HE Affociation of Ideas has a tendency to warp THE our fpeculative opinions chiefly in the three following ways:

First, by blending together in our apprehenfions, things which are really distinct in their nature; fo as to introduce perplexity and error into every process of reasoning in which they are involved.

Secondly, by misleading us in those anticipations of the future from the past, which our conftitution disposes us to form, and which are the great foundation

of our conduct in life.

Thirdly, by connecting in the mind erroneous opinions, with truths which irrefiftibly command our affent, and which we feel to be of importance to human happiness.

A fhort illustration of these remarks, will throw light on the origin of various prejudices; and may, perhaps,

fuggeft

of combination, although, perhaps, not altogether so ftriking in degree, might eafily be collected from the fubjects about which our metaphyfical fpeculations are employed. The fenfations, for inftance, which are excited in the mind by external objects, and the perceptions of material qualities which follow these fenfations, are to be diftinguifhed from each other only by long habits of patient reflexion. A clear conception of this distinction may be regarded as the key to all Dr. Reid's reafonings concerning the procefs of nature in perception; and, till it has once been rendered familiar to the reader, a great part of his writings must appear unfatisfactory and obfcure.obscure.— In truth, our progrefs in the philofophy of the human mind depends much more on that fevere and difcriminating judgment, which enables us to feparate ideas which nature or habit have intimately combined, than on acutenefs of reafoning or fertility of invention. And hence it is, that metaphysical ftudies are the best of all preparations for those philofophical pursuits which relate to the conduct of life. In none of thefe do we meet with cafual combinations fo intimate and indiffoluble as thofe which occur in metaphyfics; and he who has been accustomed to fuch discriminations as this fcience requires, will not eafily be impofed on by that confufion of ideas, which warps the judgments of the multitude in moral, religious, and political inquiries.

From the facts which have now been stated, it is eafy to conceive the manner in which the affociation of ideas has a tendency to mislead the judgment, in the first of the three cafes already enumerated. When

two

two fubjects of thought are fo intimately connected together in the mind, that we find it scarcely poffible to confider them apart; it must require no common efforts of attention, to conduct any process of reasoning which relates to either. I formerly took notice of the errors to which we are expofed in confequence of the ambiguity of words; and of the neceffity of frequently checking and correcting our general reafonings by means of particular examples; but in the cafes to which I allude at prefent, there is (if I may ufe the expreffion) an ambiguity of things; so that even when the mind is occupied about particulars, it finds it difficult to separate the proper objects of its attention from others with which it has been long accustomed to blend them. The cafes, indeed, in which fuch obftinate and invincible affociations are formed among different fubjects of thought, are not very numerous, and occur chiefly in our metaphyfical researches; but in every mind, casual combinations, of an inferior degree of strength, have an habitual effect in disturbing the intellectual powers, and are not to be conquered without perfevering exertions, of which few men are capable. The obvious effects which this tendency to combination produces on the judgment, in confounding together thofe ideas which it is the province of the metaphyfician to dif tinguish, fufficiently illuftrate the mode of its operation in those numerous inftances, in which its influence, though not so complete and striking, is equally real, and far more dangerous.

II. The affociation of ideas is a fource of fpeculative error, by misleading us in those anticipations of