Two kinds of qualities must be distinguished; the essential quality, which is a peculiarity of its being, and the mere quality, which affects the being's classification. The mere quality introduces no change in the essence, and causes none of its characteristics to disappear; but, when the being exists already, and is complete, this quality gives it a certain exterior disposition; and, whether in the case of a soul or body, adds something to it. Thus visible whiteness, which is of the very being of white lead, is not of the being of the swan, because a swan may be of some color other than white. Whiteness then completes the being of white lead, just as heat completes the being of fire. If igneousness is said to be the being of fire, whiteness is also the being of white lead. Nevertheless, the igneousness of the visible fire is heat, which constitutes the complement of its being; and whiteness plays the same part with respect to white lead. Therefore (differing according to the difference of various beings) the same things will be complements of being, and will not be qualities, or they will not be complements of being, and will be qualities; but it would not be reasonable to assert that these qualities are different according to whether or not they are complements of being, since their nature is the same. DISTINCTION BETWEEN WHATNESS AND AFFECTIONS OF BEING. We must acknowledge that the reasons which produce these things (as heat, and whiteness) are beings, if taken in their totality; but on considering their production, we see that what constitutes a whatness or quiddity (the Aristotelian "what it were to be") in the intelligible world, becomes a quality in the sense-world. Consequently, we always err on the subject of the quiddity, when we try to determine it, mistaking the simple quality for it (as thought Plato),[332] for, when we perceive a quality, the fire is not what we call fire, but a being. As to the things which arrest our gaze, we should distinguish them from the quiddity, and define them by the qualities of sense (objects); for they do not constitute the being, but the affections of being. ACTUALIZED BEING LESS PERFECT THAN ESSENCE.