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We find, by experience, that when any impression has been present with the mind, it again makes its appearance there as an idea; and this it may do after two different ways: either when, in its new appearance,[Pg 24] it retains a considerable degree of its first vivacity, and is somewhat intermediate betwixt an impression and an idea; or when it entirely loses that vivacity, and is a perfect idea. The faculty by which we repeat our impressions in the first manner, is called the memory, and the other the imagination. 'Tis evident, at first sight, that the ideas of the memory are much more lively and strong than those of the imagination, and that the former faculty paints its objects in more distinct colours, than any which are employed by the latter. When we remember any past event, the idea of it flows in upon the mind in a forcible manner; whereas, in the imagination, the perception is faint and languid, and cannot, without difficulty, be preserved by the mind steady and uniform for any considerable time. Here, then, is a sensible difference betwixt one species of ideas and another. But of this more fully hereafter.[2]
There is another difference betwixt these two kinds of ideas, which is no less evident, namely, that though neither the ideas of the memory nor imagination, neither the lively nor faint ideas, can make their appearance in the mind, unless their correspondent impressions have gone before to prepare the way for them, yet the imagination is not restrained to the same order and form with the original impressions; while the memory is in a manner tied down in that respect, without any power of variation.
'Tis evident, that the memory preserves the original form, in which its objects were presented, and that wherever we depart from it in recollecting any thing, it proceeds from some defect or imperfection in that[Pg 25] faculty. An historian may, perhaps, for the more convenient carrying on of his narration, relate an event before another to which it was in fact posterior; but then, he takes notice of this disorder, if he be exact; and, by that means, replaces the idea in its due position. 'Tis the same case in our recollection of those places and persons, with which we were formerly acquainted. The chief exercise of the memory is not to preserve the simple ideas, but their order and position. In short, this principle is supported by such a number of common and vulgar phenomena, that we may spare ourselves the trouble of insisting on it any farther.
The same evidence follows us in our second principle, of the liberty of the imagination to transpose and change its ideas. The fables we meet with in poems and romances put this entirely out of question. Nature there is totally confounded, and nothing mentioned but winged horses, fiery dragons, and monstrous giants. Nor will this liberty of the fancy appear strange, when we consider, that all our ideas are copied from our impressions, and that there are not any two impressions which are perfectly inseparable. Not to mention, that this is an evident consequence of the division of ideas into simple and complex. Wherever the imagination perceives a difference among ideas, it can easily produce a separation.
[2] Part III. Sect. 5.
As all simple ideas may be separated by the imagination, and may be united again in what form it pleases, nothing would be more unaccountable than the operations of that faculty, were it not guided by some universal principles, which render it, in some measure, uniform with itself in all times and places. Were ideas entirely loose and unconnected, chance alone would join them; and 'tis impossible the same simple ideas should fall regularly into complex ones (as they commonly do), without some bond of union among them, some associating quality, by which one idea naturally introduces another. This uniting principle among ideas is not to be considered as an inseparable connexion; for that has been already excluded from the imagination: nor yet are we to conclude, that without it the mind cannot join two ideas; for nothing is more free than that faculty: but we are only to regard it as a gentle force, which commonly prevails, and is the cause why, among other things, languages so nearly correspond to each other; Nature, in a manner, pointing out to every one those simple ideas, which are most proper to be united into a complex one. The qualities, from which this association arises, and by which the mind is, after this manner, conveyed from one idea to another, are three,[Pg 27] viz. resemblance, contiguity in time or place, and cause and effect.
I believe it will not be very necessary to prove, that these qualities produce an association among ideas, and, upon the appearance of one idea, naturally introduce another. 'Tis plain, that, in the course of our thinking, and in the constant revolution of our ideas, our imagination runs easily from one idea to any other that resembles it, and that this quality alone is to the fancy a sufficient bond and association. 'Tis likewise evident, that as the senses, in changing their objects, are necessitated to change them regularly, and take them as they lie contiguous to each other, the imagination must, by long custom, acquire the same method of thinking, and run along the parts of space and time in conceiving its objects. As to the connexion that is made by the relation of cause and effect, we shall have occasion afterwards to examine it to the bottom, and therefore shall not at present insist upon it. 'Tis sufficient to observe, that there is no relation, which produces a stronger connexion in the fancy, and makes one idea more readily recal another, than the relation of cause and effect betwixt their objects.
That we may understand the full extent of these relations, we must consider, that two objects are connected together in the imagination, not only when the one is immediately resembling, contiguous to, or the cause of the other, but also when there is interposed betwixt them a third object, which bears to both of them any of these relations. This may be carried on to a great length; though, at the same time we may observe, that each remove considerably weakens the relation. Cousins in the fourth degree are connected by causation, if I may be allowed to use that term; but not so[Pg 28] closely as brothers, much less as child and parent. In general, we may observe, that all the relations of blood depend upon cause and effect, and are esteemed near or remote, according to the number of connecting causes interposed betwixt the persons.
Of the three relations above mentioned this of causation is the most extensive. Two objects may be considered as placed in this relation, as well when one is the cause of any of the actions or motions of the other, as when the former is the cause of the existence of the latter. For as that action or motion is nothing but the object itself, considered in a certain light, and as the object continues the same in all its different situations, 'tis easy to imagine how such an influence of objects upon one another may connect them in the imagination.
We may carry this farther, and remark, not only that two objects are connected by the relation of cause and effect, when the one produces a motion or any action in the other, but also when it has a power of producing it. And this we may observe to be the source of all the relations of interest and duty, by which men influence each other in society, and are placed in the ties of government and subordination. A master is such a one as, by his situation, arising either from force or agreement, has a power of directing in certain particulars the actions of another, whom we call servant. A judge is one, who, in all disputed cases, can fix by his opinion the possession or property of any thing betwixt any members of the society. When a person is possessed of any power, there is no more required to convert it into action, but the exertion of the will; and that in every case is considered as possible, and in many as probable; especially in the case of authority,[Pg 29] where the obedience of the subject is a pleasure and advantage to the superior.
