The question has been agitated by Locke and other philosophers, "whether the soul always thinks," in other words, whether the mind, during those hours in which our limbs lie for the most part in a state of inactivity, is or is not engaged by a perpetual succession of images and impressions. This is a point that can perhaps never be settled. When the empire of sleep ceases, or when we are roused from sleep, we are often conscious that we have been to that moment busily employed with that sort of conceptions and scenes which we call dreams. And at times when, on waking, we have no such consciousness, we can never perhaps be sure that the shock that waked us, had not the effect of driving away these fugitive and unsubstantial images. There are men who are accustomed to say, they never dream. If in reality the mind of man, from the hour of his birth, must by the law of its nature be constantly occupied with sensations or images (and of the contrary we can never be sure), then these men are all their lives in the state of persons, upon whom the shock that wakes them, has the effect of driving away such fugitive and unsubstantial images.--Add to which, there may be sensations in the human subject, of a species confused and unpronounced, which never arrive at that degree of distinctness as to take the shape of what we call dreaming. So much for man in the state of sleep. But during our waking hours, our minds are very differently occupied at different periods of the day. I would particularly distinguish the two dissimilar states of the waking man, when the mind is indolent, and when it is on the alert. While I am writing this Essay, my mind may be said to be on the alert. It is on the alert, so long as I am attentively reading a book of philosophy, of argumentation, of eloquence, or of poetry. It is on the alert, so long as I am addressing a smaller or a greater audience, and endeavouring either to amuse or instruct them. It is on the alert, while in silence and solitude I endeavour to follow a train of reasoning, to marshal and arrange a connected set of ideas, or in any other way to improve my mind, to purify my conceptions, and to advance myself in any of the thousand kinds of intellectual process. It is on the alert, when I am engaged in animated conversation, whether my cue be to take a part in the reciprocation of alternate facts and remarks in society, or merely to sit an attentive listener to the facts and remarks of others. This state of the human mind may emphatically be called the state of activity and attention. So long as I am engaged in any of the ways here enumerated, or in any other equally stirring mental occupations which are not here set down, my mind is in a frame of activity.