Front Page Titles (by Subject) III.—: OF THE POWER WHICH THE MIND HAS OVER THE TRAIN OF ITS THOUGHTS - Selections from the Scottish Philosophy of Common Sense
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III.—: OF THE POWER WHICH THE MIND HAS OVER THE TRAIN OF ITS THOUGHTS - Thomas Reid, Selections from the Scottish Philosophy of Common Sense 
Selections from the Scottish Philosophy of Common Sense, edited, with an introduction by G.A. Johnston (Chicago: Open Court, 1915).
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OF THE POWER WHICH THE MIND HAS OVER THE TRAIN OF ITS THOUGHTS
By means of the Association of Ideas, a constant current of thoughts, if I may use the expression, is made to pass through the mind while we are awake. Sometimes the current is interrupted, and the thoughts diverted into a new channel, in consequence of the ideas suggested by other men, or of the objects of perception with which we are surrounded. So completely, however, is the mind in this particular subjected to physical laws, that it has been justly observed,2 we cannot by an effort of our will call up any one thought, and that the train of our ideas depends on causes which operate in a manner inexplicable by us.
This observation, although it has been censured as paradoxical, is almost self-evident; for, to call up a particular thought supposes it to be already in the mind. As I shall have frequent occasion, however, to refer to the observation afterwards, I shall endeavour to obviate the only objection which I think can reasonably be urged against it, and which is founded on that operation of the mind which is commonly called recollection or intentional memory.
It is evident, that before we attempt to recollect the particular circumstances of any event, that event in general must have been an object of our attention. We remember the outlines of the story, but cannot at first give a complete account of it. If we wish to recall these circumstances, there are only two ways in which we can proceed. We must either form different suppositions, and then consider which of these tallies best with the other circumstances of the event; or, by revolving in our mind the circumstances we remember, we must endeavour to excite the recollection of the other circumstances associated with them. The first of these processes is, properly speaking, an inference of reason, and plainly furnishes no exception to the doctrine already delivered. We have an instance of the other mode of recollection, when we are at a loss for the beginning of a sentence in reciting a composition that we do not perfectly remember, in which case we naturally repeat over, two or three times, the concluding words of the preceding sentence, in order to call up the other words which used to be connected with them in the memory. In this instance, it is evident that the circumstances we desire to remember are not recalled to the mind in immediate consequence of an exertion of volition, but are suggested by some other circumstances with which they are connected, independently of our will, by the laws of our constitution.
Notwithstanding, however, the immediate dependence of the train of our thoughts on the laws of association, it must not be imagined that the will possesses no influence over it. This influence, indeed, is not exercised directly and immediately, as we are apt to suppose on a superficial view of the subject; but it is, nevertheless, very extensive in its effects, and the different degrees in which it is possessed by different individuals, constitute some of the most striking inequalities among men, in point of intellectual capacity.
Of the powers which the mind possesses over the train of its thoughts, the most obvious is its power of singling out any one of them at pleasure, of detaining it, and of making it a particular object of attention. By doing so, we not only stop the succession that would otherwise take place, but in consequence of our bringing to view the less obvious relations among our ideas, we frequently divert the current of our thoughts into a new channel. If, for example, when I am indolent and inactive, the name of Sir Isaac Newton accidentally occur to me, it will perhaps suggest one after another the names of some other eminent mathematicians and astronomers, or of some of his illustrious contemporaries and friends, and a number of them may pass in review before me, without engaging my curiosity in any considerable degree. In a different state of mind, the name of Newton will lead my thoughts to the principal incidents of his life, and the more striking features of his character; or, if my mind be ardent and vigorous, will lead my attention to the sublime discoveries he made, and gradually engage me in some philosophical investigation. To every object, there are others which bear obvious and striking relations; and others, also, whose relation to it does not readily occur to us, unless we dwell upon it for some time, and place it before us in different points of view.
But the principal power we possess over the train of our ideas, is founded on the influence which our habits of thinking have on the laws of Association; an influence which is so great, that we may often form a pretty shrewd judgment concerning a man’s prevailing turn of thought, from the transitions he makes in conversation or in writing. It is well known, too, that by means of habit, a particular associating principle may be strengthened to such a degree, as to give us a command of all the different ideas in our mind which have a certain relation to each other, so that when any one of the class occurs to us, we have almost a certainty that it will suggest the rest. What confidence in his own powers must a speaker possess, when he rises without premeditation in a popular assembly, to amuse his audience with a lively or a humorous speech! Such a confidence, it is evident, can only arise from a long experience of the strength of particular associating principles.
To how great a degree this part of our constitution may be influenced by habit, appears from facts which are familiar to every one. A man who has an ambition to become a punster, seldom or never fails in the attainment of his object; that is, he seldom or never fails in acquiring a power which other men have not, of summoning up on a particular occasion a number of words different from each other in meaning, and resembling each other more or less in sound. I am inclined to think that even genuine wit is a habit acquired in a similar way; and that, although some individuals may from natural constitution be more fitted than others to acquire this habit, it is founded in every case on a peculiarly strong association among certain classes of our ideas, which gives the person who possesses it a command over those ideas which is denied to ordinary men. But there is no instance in which the effect of habits of association is more remarkable than in those men who possess a facility of rhyming. That a man should be able to express his thoughts perspicuously and elegantly, under the restraints which rhyme imposes, would appear to be incredible if we did not know it to be fact. Such a power implies a wonderful command both of ideas and of expression, and yet daily experience shews that it may be gained with very little practice. Pope tells us with respect to himself, that he could express himself not only more concisely but more easily in rhyme than in prose.
Nor is it only in these trifling accomplishments that we may trace the influence of habits of association. In every instance of invention, either in the fine arts, in the mechanical arts, or in the sciences, there is some new idea, or some new combination of ideas, brought to light by the inventor. This, undoubtedly, may often happen in a way which he is unable to explain; that is, his invention may be suggested to him by some lucky thought, the origin of which he is unable to trace. But when a man possesses a habitual fertility of invention in any particular art or science, and can rely, with confidence, on his inventive powers, whenever he is called upon to exert them, he must have acquired, by previous habits of study, a command over certain classes of his ideas, which enables him at pleasure to bring them under his review.1
[2 ]By Lord Kames and others.
[1 ]“Elements of the Philosophy of the Human Mind,” Works, vol. ii. pp. 266-269.