10. As regards Quality, the source of what we call a "quale," we must in the first place consider what nature it possesses in accordance with which it produces the "qualia," and whether, remaining one and the same in virtue of that common ground, it has also differences whereby it produces the variety of species. If there is no common ground and the term Quality involves many connotations, there cannot be a single genus of Quality.
What then will be the common ground in habit, disposition, passive quality, figure, shape? In light, thick and lean?
If we hold this common ground to be a power adapting itself to the forms of habits, dispositions and physical capacities, a power which gives the possessor whatever capacities he has, we have no plausible explanation of incapacities. Besides, how are figure and the shape of a given thing to be regarded as a power?
Moreover, at this, Being will have no power qua Being but only when Quality has been added to it; and the activities of those substances which are activities in the highest degree, will be traceable to Quality, although they are autonomous and owe their essential character to powers wholly their own!
Perhaps, however, qualities are conditioned by powers which are posterior to the substances as such [and so do not interfere with their essential activities]. Boxing, for example, is not a power of man qua man; reasoning is: therefore reasoning, on this hypothesis, is not quality but a natural possession of the mature human being; it therefore is called a quality only by analogy. Thus, Quality is a power which adds the property of being qualia to substances already existent.
The differences distinguishing substances from each other are called qualities only by analogy; they are, more strictly, Acts and Reason-Principles, or parts of Reason-Principles, and though they may appear merely to qualify the substance, they in fact indicate its essence.
Qualities in the true sense- those, that is, which determine qualia- being in accordance with our definition powers, will in virtue of this common ground be a kind of Reason-Principle; they will also be in a sense Forms, that is, excellences and imperfections whether of soul or of body.
But how can they all be powers? Beauty or health of soul or body, very well: but surely not ugliness, disease, weakness, incapacity. In a word, is powerlessness a power?
It may be urged that these are qualities in so far as qualia are also named after them: but may not the qualia be so called by analogy, and not in the strict sense of the single principle? Not only may the term be understood in the four ways [of Aristotle], but each of the four may have at least a twofold significance.
In the first place, Quality is not merely a question of action and passion, involving a simple distinction between the potentially active [quality] and the passive: health, disposition and habit, disease, strength and weakness are also classed as qualities. It follows that the common ground is not power, but something we have still to seek.
Again, not all qualities can be regarded as Reason-Principles: chronic disease cannot be a Reason-Principle. Perhaps, however, we must speak in such cases of privations, restricting the term "Quantities" to Ideal-Forms and powers. Thus we shall have, not a single genus, but reference only to the unity of a category. Knowledge will be regarded as a Form and a power, ignorance as a privation and powerlessness.
On the other hand, powerlessness and disease are a kind of Form; disease and vice have many powers though looking to evil.
But how can a mere failure be a power? Doubtless the truth is that every quality performs its own function independently of a standard; for in no case could it produce an effect outside of its power.
Even beauty would seem to have a power of its own. Does this apply to triangularity?
Perhaps, after all, it is not a power we must consider, but a disposition. Thus, qualities will be determined by the forms and characteristics of the object qualified: their common element, then, will be Form and ideal type, imposed upon Substance and posterior to it.
But then, how do we account for the powers? We may doubtless remark that even the natural boxer is so by being constituted in a particular way; similarly, with the man unable to box: to generalize, the quality is a characteristic non-essential. Whatever is seen to apply alike to Being and to non-Being, as do heat and whiteness and colours generally, is either different from Being- is, for example, an Act of Being- or else is some secondary of Being, derived from it, contained in it, its image and likeness.
But if Quality is determined by formation and characteristic and Reason-Principle, how explain the various cases of powerlessness and deformity? Doubtless we must think of Principles imperfectly present, as in the case of deformity. And disease- how does that imply a Reason-Principle? Here, no doubt, we must think of a principle disturbed, the Principle of health.
But it is not necessary that all qualities involve a Reason-Principle; it suffices that over and above the various kinds of disposition there exist a common element distinct from Substance, and it is what comes after the substance that constitutes Quality in an object.
But triangularity is a quality of that in which it is present; it is however no longer triangularity as such, but the triangularity present in that definite object and modified in proportion to its success in shaping that object.