The subject of locomotion is continued, and the motor principles are said to be appetite and mind; but mind in the sense rather of a perceptive or sentient than a purely intellectual faculty; and yet it is neither the centre of sensibility nor imagination, although it partakes of the nature of each of them. The imagination, which many are said to follow against judgment, is evidently the voluntary species of which man alone partakes; and the other, which is allotted to the lower animals, may be regarded as instinct. The mind, as a practical faculty, is to be distinguished from the theoretical or speculative intellect, which has for its object the discovery of truth, as the other has the preservation of the body. The argument is complicated, and made less apprehensible by the technicality and great precision of its wording: thus, τὸ ὀρεχτόν, or object desired, is food, and appetite is the stimulus or feeling of hunger which compels to move; the practical mind (διάνοια πρακτική) is the sentient faculty, and the beginning of the action, which is the satisfaction of the appetite, completes or is the last of the series. Thus, these two, the appetite and practical thought (which is sentient perception) are motors, as being both stimulus and desire, and the object desired (food, that is), acting upon the sentient perception, urges to locomotion for the attainment of it; the imagination, as an instinctive power, is said never to impel to move, save for the satisfaction of necessary wants.
Those two faculties, the appetite and the mind, appear to be the motor principles in animals—the mind, if the imagination might be set down as being a kind of thought; for many against knowledge follow their imaginings, and other animals are moved neither by thought nor calculation, but by imagination. Thus, those two faculties, mind and appetite, are locomotive powers; but, then, it is mind in the sense of a calculating and a practical faculty, and which differs from the speculative mind by the object to which it tends.