mind must be favourable to the reception or recollection of any other idea, which requires but little alteration in the state of the mind to admit it. A slight turn of the screws on which the tension of the mind depends will set it right to the point required.
When the actual state of the mind agrees, or falls in with some previous tendency, the effort which the latent idea makes to pass into a state of excitement must be more powerful than it would be without this co-operation, and where the other circumstances are indifferent must always be effectual. Thus the actual feeling of warmth will have a tendency to call up any old ideas of the same kind: e.g. a very warm spring day puts me in mind of a walk I took in a hot day last summer. Here however a difficulty occurs: for the very opposition of our feelings, as of heat and cold frequently produces an imaginary transition in the mind from the one to the other. This may be accounted for in a loose way by supposing, that the struggle between very opposite feelings producing a violent and perturbed state of mind excites attention, and makes the mind more sensible to the shock of the contrary impression than to that by which it is preoccupied, as we find that the body is more liable to be affected by any opposite extremes, as of heat and cold, immediately succeeding, and counteracting each other. Be this as it may, all things actually put us in mind of their contraries, cold of heat, day of night, &c. These three, viz. association, similarity, and contrast include, I believe, all the general sources of connection between our ideas, for as to that of cause and effect, it seems to be referable, at least, in most instances to the first class, that of common association. I hope no one will think that I mean to offer the foregoing statement as even a remote and faint approach to a satisfactory account of the matter. Every attempt of
