Quality

Plato's treatment of quality proceeds in large part by way of a doctrine he does not himself accept. In the Theaetetus, Socrates reports the teaching of those who hold that all is motion, and that from the union of an active and a passive motion there is generated a pair, the sense and the object of sense. On this account whiteness has no absolute existence. It comes to be only when the eye and the appropriate object meet, the agent having no existence until united with the patient, and the patient none until united with the agent. From such considerations, Socrates says, there arises the general reflection that there is no self-existent thing, but that everything is becoming and in relation. Whether the doctrine can be maintained is another question. A theory which denies that words keep a constant meaning from moment to moment seems to Socrates to refute itself, since it can say nothing definite in consequence.

The Timaeus offers an account of a different sort. There the sensible qualities are traced to the shapes and motions of the elemental bodies as these act upon the organs of sense, so that a sharp taste, for example, is referred to small and angular particles cutting the tongue. This manner of explanation, which grounds the qualitative in the figure and movement of the parts of matter, anticipates the reduction of quality to quantity that later atomists and mechanists undertake, a question considered more fully in the chapter on Quantity. Yet Plato does not on that account declare the qualities unreal. Of fire and water and the like, he writes, it is hard to say which of them one should call real, more than any other.

The bearing of all this upon knowledge is what chiefly concerns Plato. If a quality is nothing but what appears to each perceiver, then the Protagorean thesis that perception is knowledge would seem to follow, and with it the consequence that no two men, and no one man at two moments, could know the same thing. Plato takes the consequence to tell against the premise. What is knowable must be stable and intelligible, and the intelligible principle is not itself qualified as the sensible thing is. The Form of Fire is not hot. Whether the objects of sense have any being of their own apart from the objects of intellect is treated under the ideas of Being, Form, and Sense.

Aristotle inherits both halves of this discussion. He concurs in Plato's attitude toward the most extreme view of the professed Heracliteans, remarking that the same wine may seem sweet at one time and not sweet at another, yet the sweet, such as it is when it exists, has never changed. But he declines to place the sensible qualities outside the order of real being, and gives quality a station among the categories which Plato had reserved for what stands beyond becoming.

Aristotle draws his categories from experience, holding that they represent fundamental modes of being and are therefore the basic concepts in which thought apprehends reality. Quality stands among them as one of the ways in which something is predicated of a subject. To call a man brave or snow white is to say what the thing is like, and this, in Aristotle's view, cannot be resolved into a statement about substance, quantity, or relation. Quality is an accident, existing not by itself but in the substance it qualifies, and the enumeration of its kinds is accordingly an enumeration of the ways in which a substance may be qualified.

Four species are distinguished. The first comprises habits and dispositions, such as knowledge, virtue, and health, the more stable of these being called states and the less stable dispositions. The second comprises the inborn powers or capacities whereby a thing acts, such as the power of sensitivity in animals and of rationality in men, which, because they belong to a nature as such, are sometimes called properties. The third is shape or figure, and the fourth the affective qualities, colors and sounds, textures, odors, tastes, and the thermal qualities of hot and cold. The first two, it should be noted, are not directly sensible, so that on Aristotle's own division not every quality is an object of sense.

The marks by which quality is set apart from substance occupy him at some length. One and the same substance can receive contrary qualities, being at one time white and at another black, whereas the qualities themselves do not pass into one another; the sweet thing may become sour, but sweetness never becomes sourness. Qualities admit of variation in degree, one white being whiter than another, while one man cannot be more man than another. Yet neither mark holds universally, since shape does not vary in degree and not every quality has a contrary, and Aristotle concludes that one characteristic alone is peculiar to quality. Quality is the ground on which things are called like or unlike, as quantity is the ground on which they are called equal or unequal. Contrariety and correlation are treated more fully under the idea of Opposition, and the comparison of the two categories under Quantity.

The fourfold classification governs the discussion of quality for a long period, and Aquinas adopts it with little alteration while extending the analysis of habit. What the classification leaves unsettled is the standing of the sensible qualities in the bodies said to possess them. Aristotle assigns colors and sounds the same actuality he assigns shape and motion, and criticizes the atomists for granting objective reality to some sensible attributes while denying it to others. Hobbes and Descartes take the opposite course, reserving to body only what Aristotle would call quantity, and Locke divides the qualities into two sorts on precisely this line.

Aquinas takes over Aristotle's enumeration of the species of quality and states the character common to them. Quality, he writes, implies a certain mode of substance. It answers neither the question what a thing is, which belongs to substance, nor the question how much, which belongs to quantity, but the question in what manner a thing exists and acts. Natural qualities, he adds, may be in the intellectual part of a thing's nature or in the body and its powers, from which it follows that some qualities are sensible and some are not. The habits and dispositions of a man, and the inborn powers whereby men and other animals act to develop their natures, fall in the latter class, while colors, sounds, and the thermal qualities fall in the former.

Habit occupies the largest place in his treatment. A habit is a disposition, more settled than those dispositions which are easily lost, whereby a thing is disposed well or ill with respect to its nature or its operation. Virtue on this account is a habit of the soul, and vice a habit likewise, the one disposing well and the other ill; knowledge is a habit of the intellect. Aquinas distinguishes habits from the natural powers they perfect. The power of understanding belongs to the soul by nature, whereas the habit is acquired by act or, in the case of the theological virtues, infused. The power is what enables a man to reason at all; the habit is what enables him to reason well and readily. The moral consequences of this analysis are pursued under the ideas of Habit and Virtue.

The relation of quality to quantity gives rise to a further difficulty which Aquinas attempts to meet. Since a body may be whiter at one time than at another, quality would seem to admit of a certain amount, though quality is not quantity and one accident cannot exist in another. He answers by distinguishing the dimensive quantity of bodies from what he calls the virtual quantity of qualities, this last being the degree or intensity which nonquantitative attributes may possess, whether personal qualities such as the virtues or corporeal ones such as colors. In the order of the accidents he holds that quantity is the proximate subject of the qualities that cause alteration, as surface is of color, and that quantity is in substance before sensible qualities are. Whether this priority extends to every kind of quality, or only to the sensible ones, remains a question, since the qualities of the intellectual part appear to rest on no quantity at all.

The doctrine joins the analysis of being to the analysis of conduct, since the same category that covers color and heat covers also the virtues by which a man is said to be good. It rests, however, on the distinction between substance and accident, and on the conception of the soul as that in virtue of which a living thing has its vital powers. When Hobbes and Descartes deny that the sensible qualities are in bodies at all, and assign to body only extension and motion, the category itself is narrowed, and the account of habit as a modification of the soul is not readily restated in the newer vocabulary. The fortunes of the underlying distinction are considered under the ideas of Being and Matter.

Hobbes regards the sensible qualities as feelings in us, the seemings or fancies of sense. The cause of sense, he holds, is the external body which presses the organ proper to each sense, and this pressure is continued inward by the nerves and other strings and membranes of the body until it reaches the brain and heart, where it causes a resistance or counter-pressure. That endeavor outward appears to us as some quality, as light or color to the eye, as sound to the ear, as odor to the nostril. The qualities called sensible, in his account, are in the object that causes them nothing but so many several motions of the matter by which it presses our organs diversely. The object is one thing and the fancy another.

Hobbes states the consequence in the form of a rule about the use of names. Among the kinds of absurd assertion he enumerates, one consists in giving the names of the accidents of bodies without us to the accidents of our own bodies, as they do who say that the color is in the body or the sound in the air. What belongs to bodies, on this reckoning, is magnitude, figure, and motion, and these are attributes which Aristotle would have classed under quantity rather than quality. Bodies accordingly differ from one another only quantitatively, and qualitative difference occurs only in sense or in thought. The doctrine leaves no room for substantial forms or for real heat in the fire, and natural philosophy becomes the science of bodies in motion.

Whether this account can be sustained turns on questions belonging to other parts of the tradition. It presupposes a theory of sensation in which the sensible species is replaced by transmitted motion, a matter treated more fully under the idea of Sense, and a theory of matter which admits only the quantitative attributes, treated under Matter and Quantity. Aristotle's objection to the atomists bears upon it directly, since he denies that there is any ground for granting objective reality to some sensible attributes, such as figure and motion, while withholding it from colors, sounds, and odors. The objection from the other side, urged later by Berkeley, is that the attributes Hobbes retains are no better situated than those he discards.

Hobbes states in a summary way a position which Descartes reaches by a different route and which Locke afterward divides into two parts, retaining for body the qualities Hobbes retains and assigning to the remainder the status of powers to produce ideas in us. The reduction of the sensible world to matter in motion also connects the discussion of quality with the account of mind and of the passions given elsewhere in the Leviathan, since imagination, memory, and appetite are explained by Hobbes as decaying or continuing motions of the same kind.

Descartes derives his account of quality from his conception of substance. Nothing belongs to the nature or essence of body, he says, except length, breadth, and depth, admitting of various shapes and various motions. Colors, odors, savors, and the rest are merely sensations existing in thought, and differ no less from bodies than pain differs from the shape and motion of the instrument which inflicts it. The comparison with pain is meant to show that a body may have the power to produce in us a modification of thought without possessing anything resembling that modification. What follows from extension, such as figure, size, situation, and divisibility, is in the body; what does not follow from it is referred to the union of mind and body rather than to the object.

The argument of the Meditations proceeds by way of the piece of wax. Heated, the wax alters in every sensible quality, its color, its scent, its hardness, and its shape, and yet it is judged to be the same wax. What remains through the alteration is something extended, flexible, and movable, and this remainder is apprehended, Descartes maintains, by the understanding and not by sense or imagination. The sensible qualities are not on that account useless. They serve the preservation of the composite of mind and body, warning of what is harmful and directing us toward what is beneficial. They are not, however, evidence of the nature of matter, which is known clearly and distinctly through extension alone.

On one point Descartes agrees with the tradition he otherwise opposes. To assert the existence of real accidents, by which he means the existence of qualities or quantities apart from substances, is in his view to deny the distinction between substance and accident altogether. Substance, he writes, can never be conceived after the fashion of accidents, nor derive its reality from them, and no reality can be ascribed to accidents which is not taken from the idea of substance. Qualities, in whatever manner they exist, exist in something. The disagreement with Aristotle and Aquinas concerns not this principle but the question of which attributes belong to bodies and which to minds, a question inseparable from the doctrine of the two substances treated under the ideas of Matter and Mind.

Locke takes from Descartes and from Hobbes the substance of the division, though he states it differently. Where Descartes assigns to bodies only what he counts as attributes of extension, and denies that colors and savors are in them at all, Locke calls both sorts qualities of bodies, the one original and the other a power to produce sensations in us. The criticism to which the Cartesian position is exposed takes two forms. Aristotle's, urged in advance of it, is that no ground has been given for treating the proper objects of the several senses differently from the common ones. Berkeley's, urged afterward, is that the arguments which remove color from bodies remove extension and figure as well.

Locke's statement of the distinction is preceded by a distinction between the qualities of things and the ideas in our minds. A snowball, he writes, has the power to produce in us the idea of white, cold, and round. The powers to produce those ideas, as they are in the snowball, he calls qualities; as they are sensations or perceptions in our understandings, he calls them ideas. He uses the word quality with almost the generality that Descartes and Aristotle give to the word accident, so that his division falls within the class of attributes generally rather than within the narrower Aristotelian category. The original or primary qualities of body, which sense finds in every particle of matter having bulk enough to be perceived and which the mind finds inseparable from every particle however small, he enumerates as solidity, extension, figure, motion or rest, and number, a list closely resembling Newton's enumeration of the universal qualities of all bodies whatsoever.

The secondary qualities, such as colors, sounds, and tastes, are said to be nothing in the objects themselves but powers to produce various sensations in us by their primary qualities, that is, by the bulk, figure, texture, and motion of their insensible parts. The sensation of pain is offered in confirmation. The piece of steel which by its corporeal properties has the power to produce pain in us does not itself possess the quality of pain, and neither, on Locke's account, does it possess anything answering to the ideas of blueness or coldness which it produces, beyond the power to produce them. The whole rests on a corpuscularian hypothesis about the constitution of matter, a hypothesis whose standing is considered under the idea of Matter.

Locke nevertheless maintains that all our simple ideas of quality, of the secondary no less than of the primary, agree with the reality of things. By agreement he does not mean resemblance in the sense of copying, and he therefore thinks he can deny any likeness between sensations of color or taste and the secondary qualities of bodies while still saying that if sugar produces in us the ideas we call whiteness and sweetness, there is a power in sugar to produce those ideas. How we know that our ideas of the primary qualities do resemble their patterns he does not undertake to demonstrate. That question is the one Berkeley and Hume press.

Locke's terms have organized the modern discussion, though his point has been given opposite implications by different readers. Earlier thinkers who do not speak of primary and secondary qualities, among them Descartes, Hobbes, and Lucretius, attribute to bodies only what Locke calls primary and allow the rest no existence outside the mind. Berkeley moves in the contrary direction, arguing that the primary qualities are no more separable from perception than the secondary ones. Aristotle's division of the objects of sense into proper and common sensibles covers much the same ground on a different principle, and is treated under the idea of Sense.

Hume professes to adopt Berkeley's reasoning on this head. It is universally allowed by modern enquirers, he observes, that all the sensible qualities of objects, such as hard and soft, hot and cold, white and black, are merely secondary and exist not in the objects themselves but as perceptions of the mind, without any external archetype or model which they represent. If this be allowed with regard to the secondary qualities, he argues, it must also follow with regard to the supposed primary qualities of extension and solidity. The idea of extension is acquired from the senses of sight and feeling, and if the qualities perceived by those senses are in the mind and not in the object, the same conclusion must reach the idea of extension.

Nothing can save us from this conclusion, Hume says, but the assertion that the ideas of the primary qualities are attained by abstraction, an opinion which upon accurate examination he finds unintelligible and even absurd. The appeal to abstraction is unavailable to him because he denies that we can form a general idea of extension divested of every degree of color and solidity; every idea, on his principles, is a copy of some particular impression and retains its particularity. The doctrine of abstraction on which the objection turns is discussed under the ideas of Idea and Universal.

The conclusion is offered as a report of what philosophical reasoning yields rather than as a rule of life. Belief in an enduring world of bodies possessing determinate properties is, in Hume's account, natural and unavoidable, and no argument dislodges it in practice. What the argument dislodges is the claim that reason can mark off a class of attributes belonging to things from a class belonging to us. The Treatise goes further, describing the elements of experience without reference to any substance in which they inhere, so that what is given may as fitly be called qualities related by succession and contiguity as by any other name. Whether qualities can subsist in this manner, without a subject, is the question raised at the outset of the chapter and treated under the idea of Being.

Kant treats this impasse as the occasion for a change in the form of the question, asking not which qualities inhere in things as they are in themselves but how quality enters into the structure of possible experience. One point, however, seems to survive the controversy in whatever form it is conducted. As James remarks, the sensible qualities are the elements of human experience on either hypothesis we may make concerning the relation of the feelings to the realities at whose touch they become alive.

Kant disagrees with Aristotle's listing of the categories and calls his own transcendental, to indicate that they are not drawn from experience but are a priori forms of thought which determine the structure of all possible experience. Under the heading of quality he places reality, negation, and limitation. Reality answers to the presence of sensation in an appearance, negation to its absence, and limitation to a degree lying between the two. Since on his view we have no cognition of things as they are apart from the conditions under which they are given to us, the question which of the qualities inhere in objects independently of perception is one he declines to entertain in that form. What remains to be asked is how quality enters into the structure of experience.

The answer is set out in the Anticipations of Perception. In all appearances, Kant holds, the real which is an object of sensation has intensive magnitude, that is, a degree. Warmth may be more or less intense, a light brighter or dimmer, a sound louder or fainter, and between any given degree and its complete absence there is a continuous connection of possible smaller degrees. This is asserted as known in advance of any particular perception, which is why the principle is called an anticipation. Sensation is said to fill time as extensive magnitude fills space, but by degrees of reality rather than by the addition of parts to parts.

The doctrine bears on the older question about the amount or degree of a quality which Aristotle raised and Aquinas met with the notion of a virtual quantity. Kant, like them, denies that intensity is a quantity of the same kind as bulk or number, since the degree of a sensation is apprehended in an instant and not by the successive synthesis of homogeneous parts. Where the earlier writers assign the degree to the quality as it exists in the substance, Kant assigns it to the appearance and to the form under which appearances are received. The comparison of the two sorts of magnitude is treated further under the idea of Quantity, and the standing of things in themselves under Being and Knowledge.

The distinction between primary and secondary qualities loses its footing on this account, though for a reason different from Hume's. Kant does not deny that objects affect us; he denies that our representations can be compared with things as they are apart from all representation, so that the question which class of representations copies its object cannot be raised. Hegel, who follows him in the order of exposition, objects that the categories so understood remain external to their content, and undertakes to derive quality from the concept of being itself rather than from the constitution of the knowing subject.

Hegel begins the Science of Logic with being, taken as wholly indeterminate, and finds that being so taken is indistinguishable from nothing. The first determination through which thought passes beyond that emptiness is quality. Quality, in his account, is not an accident affixed to a substance already constituted, but the determinateness of being itself, so bound up with what a thing is that a thing ceases to be what it is if it loses its quality. The point may be put by saying that a determination which can be removed while the subject remains is not, in Hegel's sense, its quality. Whether such a conception can be reconciled with the older doctrine of accidents inhering in substance is a question that belongs to the idea of Being.

The order in which quality and quantity stand is thus reversed from the order proposed by those who make quantity the proximate subject of qualities. On Hegel's view a thing must be somewhat, that is, qualitatively determined, before it can be counted or measured, and quantity is described as determinateness rendered indifferent to being, a quality whose alteration leaves the thing what it was. The two are afterward united in the category of measure, in which a quantitative change carried far enough issues in a change of quality. This treatment of the relation between the two categories may be compared with the discussions considered under the idea of Quantity, where the priority of the one to the other is disputed on other grounds.

The development does not rest in quality. Every determinate quality excludes what it is not, so that whatever is something has its limit and stands over against an other. The limit, in Hegel's analysis, both constitutes the thing and points beyond it, and finite quality is on that account unstable, passing over into what it excludes. The movement from being through determinate being to finitude and the infinite is offered as a movement of the concept rather than as a report of observation, and it connects the treatment of quality with the account of change and of opposition given under those ideas.

With Hegel the term returns to the place it occupied before the moderns narrowed it to the sensible attributes of body. Quality is treated neither as a property added to a substance nor as a sensation referred to an object by the perceiver, but as the first determination in which the concept of being acquires content. The controversy over the objectivity of sense qualities, which occupies Locke, Berkeley, and Hume, is thereby set aside rather than settled, since the qualities under discussion in the Logic are categories of thought and not colors and sounds. Whether the two inquiries can be brought together is among the questions the tradition leaves open.