But, if possible, to leave no doubt on this important point, let us enquire into the nature of that remembrance left by our sensations when they are accompanied with ideas. Pain and pleasure are pure sensations, and the strongest of any, yet we but feebly recollect them, and with confusion. All we remember is, that we were pleased or hurt; but this remembrance is not distinct; we cannot represent to ourselves either the kind, the degree, or the duration of those sensations by which we had been so violently agitated; and the less are we capable of representing those we had but seldom felt. A pain, for example, which we have experienced but once, which only lasted a few minutes, and differed from all former pains, would be soon forgotten; we might recollect we felt great pain, yet, though we distinctly recollected the circumstances which accompanied it, and the period at which it happened, we should have but an imperfect remembrance of the pain itself.
Why is almost every thing forgotten that passed during our infancy? Why have old men a more distinct remembrance of what happened in their prime of life than what occurred in their more advanced years? Can there be a stronger proof that sensations alone are not sufficient to produce memory, and that it exists solely in the train of ideas which our minds derive from those sensations? In infancy the sensations are as lively and rapid as in manhood, yet they leave few or no traces, because at this era the power of reflection, which alone can form ideas is almost totally inactive; and because in the moments it does act, its comparisons are only superficial. In manhood reason is completely developed, because the power of reflection is in full exercise; we then derive from our sensations every possible advantage, and form many orders of ideas, and chains of thought, whereof each, from being often revolved, forms so durable and indelible an impression, that when old age comes on, those very ideas present themselves with more force than those derived from present sensations, because at that period the sensations are feeble, slow and dull, and the mind itself partakes of the languor of the body. In infancy, the time present is every thing; in manhood, we equally enjoy the past, the present and the future; in old age we have little sense of the present, we turn our eyes to the future, and exist in the past. In the infant that prattles, and the old man that dotes, reason is alike imperfect, because they are alike void of ideas; the former is as yet unable to form them, and the latter has ceased.