Amid all this variety of feelings, with whatever rapidity the changes may succeed each other, and however opposite they may seem, we have still the most undoubting belief, that it is the same individual mind, which is thus affected in various ways. The pleasure, which is felt at one moment, has indeed little apparent relation to the pain that was perhaps felt a few moments before; and the knowledge of a subject, which we possess, after having reflected on it fully, has equally little resemblance to our state of doubt when we began to inquire, or the total ignorance and indifference which preceded the first doubt that we felt. It is the same individual mind, however, which, in all these instances, is pleased and pained, is ignorant, doubts, reflects, knows. There is something “changed in all, and yet in all the same,” which at once constitutes the thoughts and emotions of the hour, and yet _outlives_ them,--something, which, from the temporary agitations of passion, rises, unaltered and everlasting, like the pyramid, that lifts still the same point to heaven, amid the sands and whirlwinds of the desert. The consideration of the mind, as one substance, capable of existing in a variety of states, according as it is variously affected, and constituting, in these different states, all the complex phenomena of thought and feeling, necessarily involves the consideration of _consciousness_, and of _personal identity_. To the examination of these, accordingly, I now proceed, as essential to all the inquiries and speculations, in which we are afterwards to be engaged; since, whatever powers or susceptibilities we may consider as attributes of the mind, this consideration must always suppose the existence of certain phenomena, of which we are conscious, and the identity of the sentient or thinking principle, in which that consciousness resides, and to which all the varieties of those ever-changing feelings, which form the subjects of our inquiry, are collectively to be referred. Our first inquiry, then, is into the nature of CONSCIOUSNESS.