Opus Majus of Roger Bacon, Vol. II (Burke English trans.)

heard a lion before nor seen one. The same is true in regard to many things that are hurtful and contrary to the constitution or complexion i.e., temperament or physical disposition of animals. The same principle holds good as regards what is useful and in conformity with their natures. For although a lamb may never have seen another lamb before, it runs to one and willingly remains with it, and the same is true concerning other animals. Brutes, therefore, have some perception of things advantageous and things harmful. There is then something sensible in them besides the twenty-nine properties mentioned above and besides those that are reduced to them. For there must be something more active and productive of change in the sentient body than light and color, because it not only causes apprehension but also a state of fear or love or flight or delay. This is the property of the complexion belonging to each object by which it is assimilated to others in a nature special or general. Through this quality things agree, are strengthened and invigorated, or differ and oppose one another and are mutually harmful. Wherefore not only do light and color produce their forms and impressions, but to a far greater degree do the properties of complexions—nay, the very natures of things as regards their substance, agreeing or disagreeing with one another—produce strong impressions, which change greatly the sensitive soul, so that it is moved to states of fear, horror, flight, or the opposites. These forms or impressions coming from things, although they change and alter special senses and the common sense and imagination, just as they do the air through which they pass, yet no one of those faculties of the soul judges concerning these impressions. Of necessity, a far nobler and more powerful faculty of the sensitive soul does, which is called estimation or the estimative faculty, as Avicenna states in the first book On the Soul; a faculty which he says perceives the insensible forms connected with sensible matter. Sensible matter is spoken of here as that which is apprehended by the special senses and by the common sense, as are the aforesaid twenty-nine. We call insensible form that which is not taken cognizance of by those senses of themselves, since they are commonly called senses, although other faculties of the sensitive soul may equally well be called senses, should we wish so to name them, because they are parts of the sensitive soul. For every part of the sensitive soul can be called