As writers, for the most part, define Vital Principle by two different faculties, by locomotion and thought, judgment and sensibility, it would seem as though thought and reflexion are by them considered to be some kind of sensation; for, in both cases, the Vital Principle both discerns and recognises something. Thus, the ancients affirm that reflexion is identical with feeling; and Empedocles has said, "man's intelligence is enlarged by what is present," and, elsewhere, "hence, man derives his power of reflecting upon different subjects;" so Homer's words, "such is the mind" do but express the same idea. All these writers assume, in fact, that thinking, like feeling, is corporeal, and that Like is perceived and comprehended by Like, as was explained in our opening chapters. But yet it was incumbent upon them to have spoken, at the same time, upon the liability to error through the senses; for this belongs, more peculiarly, to animals, and Vital Principle remains subject to it during the greater portion of existence. On which account, either all appearances are, as some of those writers maintain, necessarily, true, or else error is caused by contact of the unlike, which is the opposite of the opinion, that like is recognised by like; and the error from contraries seems to be identical with the knowledge of contraries. It is manifest that feeling is not identical with reflexion; for, while the former belongs to all creatures, the latter has been imparted only to a few. Neither is thinking, that faculty to which belongs the sense of right and wrong, (the right comprehending judgment, knowledge, and sound opinion, the wrong comprehending their contraries,) to be confounded with feeling—for sensation, being derived from particulars, is ever true, and belongs to all animals; but the judgment may be wrong, and is imparted only to such as have reason. Imagination, in fact, is neither sensation nor judgment, and yet it is not called up without sensation, just as, without sensation, there can be no conception; but it is manifest that imagination is not conception. Imagination depends, in fact, but upon ourselves, as we can, at will, call it up (since it is in our own power to place images before the eyes, as do they who, for mnemonic aids, by laying down objects, form symbols); but to form an opinion does not depend upon ourselves, and then every opinion is, of necessity, either true or false. Whenever, besides, we may have an opinion upon any terrible and fearful incident, we are straightway affected as if it were a reality, just as We are when we think upon any desperate deed; but, under imagination, we become simple spectators, as it were, of a pictorial representation of terrible or daring achievements. There are, in conception itself, the distinctions of knowledge, opinion, reflexion, and their contraries, of which we shall speak elsewhere. With respect to thinking, since it is different from feeling, and feeling seems, in part, to be imagination and, in part, conception, let us here define imagination, and then proceed to the consideration of the other faculty.
If imagination be a faculty by which we say that an image of some kind, and that not merely in the sense of a metaphor, is called up within us, then it is to be ranged among those faculties or powers, such as feeling, opinion, knowledge, mind, by which we form judgments and determine what may be true or false.
It is clear from what follows, that imagination is not sensation ; for sensation is either a faculty or an act, such as sight, and seeing, but an image is sometimes apparent to us without either faculty or act, as phantoms in dreams for instance; and then sensation is ever present, which is not the case with the imagination. If, moreover, imagination were in act identical with sensation, we should have to admit that it must belong to all irrational creatures, but this does not seem to be the case with the ant, bee, or worm; and then sensations are always true, but imaginings are for the most part false. Hence, we do not say, when accurately examining any object, that we imagine to be so or so, a man for instance, but we so express ourselves rather when we do not clearly perceive what the object is, and when the perception may be true or false; when, to use a former expression, the object appears to us as landscapes do to the purblind.
Neither can imagination be regarded as one of those faculties, such as knowledge and mind, which are always true, for it admits of being false as well; and it remains for us to consider whether it is opinion, since opinion may be both true and false. But belief follows upon opinion, (as it is not admissible that an individual should not believe in that upon which he has an opinion,) and belief belongs to no irrational creature although imagination is imparted to many. Belief, besides, is an attendant upon every opinion, as persuasion is upon belief, and reason alone can persuade ; but although imagination belongs to some irrational creatures, reason has been given to none. It is manifest, then, that imagination can neither be opinion with or through sensation, nor a combination of opinion with sensation; and for the same reasons evident, that opinion is from nothing else but that from which sensation is derived. By which I mean, if imagination be the combination of an opinion of whiteness and a sensation of whiteness, and not of an opinion of goodness with a sensation of whiteness, then to imagine is to think upon what has been sensually perceived, and that not accidentally. But there are appearances which are fallacious, although our conception of them at the time may be true, as the sun, for instance, appears to be a foot in diameter, and yet we are satisfied that it is larger than the earth; and in such a case it happens either that the true opinion of the sun's dimension must have been cast aside, or else, while the sun remains as it was and the true opinion has neither been forgotten nor changed, that the opinion is at once both true and false. But the opinion is simply false when it escapes us that the thing seen is altered. It is evident, then, that imagination can neither be any one, nor be derived from any one of those faculties.
Since one object having been set in motion can communicate motion to another, and since imagination seems to be a kind of motion, and never to be produced without sensation, or in other than sentient creatures, or without the objects of sentient perception, and since, on the other hand, motion can be produced by the act of sensation, and this motion must of necessity be equal to the impression, it may be admitted that the motion of imagination can neither be produced without sensation, nor in other than sentient beings; that beings endowed with it act and are acted upon in many ways, and that its manifestations are both true and false. This latter alternative happens thus: the sensation which is derived from the objects peculiar to each sense is true, or it involves the smallest amount of error; but when, in the second place, such objects are perceived in their accidents, there is room for fallacy; when for instance, something is said to be white, there is no fallacy, but when that object is particularised and said to be this or that, the perception may be fallacious. There is, in the third place, liability to error in our perception of common properties, and sequences in the accidents referrible to particular bodies—accidents, I mean, such as motion and magnitude, which are referrible to all bodies, and from which there is peculiar liability to error through the senses. But the motion produced by the act of sensation will differ from the sensation derived from these three modes of sensation—the first, while sensation is yet present, must be true; but the others, whether sensation be present or not, may be fallacious, and more especially, when the objects causative of sensation may have been withdrawn. If, then, imagination alone fulfil all the conditions indicated, and if it be all that has been said, it may be defined as motion produced by sensation in action. And since vision is a sense above all others, imagination has derived its appellation from light, because without light there is no vision; and owing to its being an abiding faculty and like sensations, animals perform many of their actions through it. Some animals are so influenced from being irrational; and others, as man, from having their understanding eclipsed, at times, by passion, disorder, or sleep.
Let this much, however, suffice for the inquiry into imagination, for shewing what it is, and for what purposes it has been imparted.