V. CHA P. which fleep feems to be partial; that is, when the mind lofes its influence over fome powers, and retains it over others. In the cafe of the fomnambuli, it retains its power over the limbs, but it poffeffes no influence over its own thoughts, and scarcely 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 meafure fufpended; either in confequence of a particular idea, which engroffes the attention, to the exclufion 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 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 in the fame manner. By means of this fuppofition of a partial fleep, any apparent exceptions which the history of dreams may afford to the ral principles already stated, admit of an eafy explanation. gene UPON reviewing the foregoing obfervations, it does not occur to me, that I have in any inftance tranfgreffed thofe rules of philofophifing, which, fince the time of Newton, are commonly appealed to, as the tefts 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 V. of the causes to which I have referred them. I have not fup- CHA P. pofed, 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 exercife of others is fufpended: and I have deduced fynthetically, the known phenomena of dreaming, from the operation of a particular class of our faculties, uncorrected by the operation of another. I flatter myself, therefore, that this inquiry will not only throw fome light on the ftate 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]. 340 CHAPTER FIFTH. PART SE CON D. Of the Influence of Affociation on the Intellectual and on the Active Powers. CHAP. SECTION I Of the Influence of cafual Affociations on our Speculative Conclufions. HE Affociation of Ideas has a tendency to warp our fpeculative opinions chiefly in the three following ways: FIRST, by blending together in our apprehenfions, things which are really diftinct 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, 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 SHORT illuftration of these remarks, will throw light on the origin of various prejudices; and may, perhaps, suggest some practical hints with refpect to the conduct of the understanding. I. I FORMERLY had occafion to mention feveral instances of very intimate affociations formed between two ideas which have no necessary connexion with each other. One of the most remarkable is, that which exists in every person's mind between the notions of colour and of extenfion. The former of these words expreffes (at least in the sense in which we commonly employ it) a fenfation in the mind; the latter denotes a quality of an external object; fo that there is, in fact, no more connexion between the two notions, than between thofe of pain and of folidity*; and yet, in confequence of our always perceiving extenfion, at the fame time at which the fenfation of colour is excited in the mind, we find it impoffible to think of that fenfation, without conceiving extenfion along with it. ANOTHER intimate affociation is formed in every mind between the ideas of space and of time. When we think of an * See Note [P]. interval V. CHA P. interval of duration, we always conceive it as fomething anaPART II. logous to a line, and we apply the fame language to both fubjects. We speak of a long and short time, as well as of a long and short distance; and we are not confcious of any metaphor in doing so. Nay, so very perfect does the analogy appear to us, that Boscovich mentions it as a curious circumstance, that extenfion should have three dimenfions, and duration only one. THIS apprehended analogy feems to be founded wholly on an affociation between the ideas of space and of time, arising from our always measuring the one of these qualities by the other. We measure time by motion, and motion by extenfion. In an hour, the hand of the clock moves over a certain space; in two hours, over double the space; and fo on. Hence the ideas of space and of time become very intimately united, and we apply to the latter the words long and short, before and after, in the fame manner as to the former. THE apprehended analogy between the relation which the different notes in the scale of music bear to each other, and the relation of fuperiority and inferiority, in refpect of pofition, among material objects, arifes alfo from an accidental affociation of ideas. WHAT this affociation is founded upon, I shall not take upon me to determine; but that it is the effect of accident, appears clearly from this, that it has not only been confined to parti cular |