for this is the definition of art, a system of comprehensions well practised with reference to some desirable end, the word desirable being very properly added by reason of the abundance of evil arts. But the definition of science is a safe and firm comprehension, which, through reason, is not liable to any error. Therefore we call music and grammar, and other pursuits, arts; for those also who are made perfect in them, as musicians, or grammarians, are called artists. But we call philosophy and the other virtues, sciences, and those who are possessed of the knowledge of them we call scientific; for they are prudent, and temperate, and philosophical, not one of whom is ever deceived in the doctrines of a philosophy which he himself has cultivated, any more than the artists, whom I have mentioned before, err in their speculations with respect to their indifferent arts.
 For as the eyes see, and still the mind sees more clearly by means of the eyes; and as the ears hear, but nevertheless the mind hears better through the medium of the ears; and as the nostrils smell, and yet the soul smells more precisely through the instrumentality of the nostrils; and in like manner, as the other external senses comprehend their respective appropriate objects, still the mind comprehends them also more purely and distinctly by their ministration. For to speak properly, it is the mind which is the eye of eyes, the hearing of hearing, and the more pure external sense of each of the external senses, using them as ministers in a court of justice, and itself deciding on the nature of the objects submitted to it, so as to approve of some and to reject others. In the same way, those that are called the intermediate arts, resembling the faculties of the body, indulge in contemplations according to certain simple observations of them, but the sciences do so with greater accuracy and with an exceedingly careful investigation.
 For the same relation that the mind bears to the outward

 Genesis xvi. 4. 
 
sense, that same does science bear towards art; for, as has been said before, the soul is as it were the outward sense of the outward sense; therefore each of them has attracted to itself some slight things of nature, concerning which it labours and occupies itself, geometry having appropriated lines, and music sounds, and philosophy the whole nature of existing things. For this world is its subject matter, and so is the whole essence, both visible and invisible, of existing things.
 What then is there wonderful if the soul, which sees both the whole and the parts, sees them too better than they do, as if it were furnished with larger and more acute eyes? Very naturally, therefore, proper philosophy will behold intermediate instruction its handmaiden, and see that she is pregnant, more than the other will see that she is.