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 history 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 transgreffed those rules of philosophising, 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 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 confcious 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 illuftrate the mutual adaptation and fubferviency which exists 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 Affociations 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; so 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 difpofes us to form, and which are the foundation great 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 illuftration of these remarks, will throw light on the origin of various prejudices; and may, perhaps,

fuggeft

fuggeft fome practical hints with respect to the conduct of the understanding.

I. I formerly had occafion to mention feveral inftances of very intimate affociations formed between two ideas which have no neceffary connexion with each other. One of the most remarkable is, that which exifts in every perfon's mind between the notions of colour and of extenfion. The former of these words expreffes (at least in the fense in which we commonly employ it) a fenfation in the mind; the latter denotes a quality of an external object; so 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 interval of duration, we always conceive it as fomething analogous to a line, and we apply the fame language to both fubjects. We fpeak of a long and fhort time, as well as of a long and fhort distance; and we are not confcious of any metaphor in doing so. Nay, fo very perfect does the analogy appear to us, that Bofcovich mentions it as a curious circumstance, that extenfion fhould have three dimenfions, and duration only one.

This apprehended analogy feems to be founded wholly on an affociation between the ideas of space and

See Note [P].

of

of

of time, arifing from our always measuring the one o thefe quantities by the other. We measure time by motion, and motion by extension. In an hour, the hand of the clock moves over a certain fpace'; in two hours, over double the fpace; and fo on. Hence the ideas of fpace and of time become very intimately united, and we apply to the latter the words long and fhort, before and after, in the fame manner as to the former.

The apprehended analogy between the relation which the different notes in the fcale of music bear to each other, and the relation of fuperiority and inferio rity, in respect of pofition, among material objects, arises alfo from an accidental affociation of ideas.

What this affociation is founded upon, I fhall 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 particular ages and nations; but is the very reverse of an affsociation which was once equally prevalent. It is obferved by Dr. Gregory, in the preface to his edition of Euclid's works, that the more ancient of the Greek writers looked upon grave founds as high, and acute ones as low; and that the prefent mode of expreffion on that fubject, was an innovation introduced at a later period *.

In the inftances which have now been mentioned, our habit of combining the notions of two things, becomes fo ftrong, that we find it impoffible to think of the one, without thinking at the fame time of the other. Various other examples of the fame fpecies

See Note [Q].

of

of combination, although, perhaps, not altogether fo ftriking in degree, might eafily be collected from the fubjects about which our metaphysical speculations are employed. The fenfations, for inftance, which are excited in the mind by external objects, and the perceptions of material qualities which follow these sensations, are to be distinguished from each other only by long habits of patient reflexion. A clear conception of this diftinction 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 muft. appear unfatisfactory and obfcure.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 acuteness of reasoning or fertility of invention. And hence it is, that metaphyfical studies 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 those which occur in metaphyfics; and he who has been accuftomed to fuch difcriminations as this fcience requires, will not eafily be impofed on by that confusion of ideas, which warps the judgments of the multitude in moral, religious, and political inquiries.

From the facts which have now been ftated, 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