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Basically a method for establishing the truth of man's beliefs; varying estimates of its value for this purpose have been given in the history of thought. This article is concerned mainly with the nature and estimate of dialectics in Aristotle, who considered it capable of rendering beliefs only probable. His position is explained in contrast to that of Plato, who regarded dialectics as yielding the surest kind of knowledge. Since a method is determined by the subject matter on which it is used, the difference between the two is accounted for in terms of their different views of the real. The value of dialectics in modern thought is then briefly indicated.

Plato. One of the earliest extended treatments of dialectics occurs in plato as part of his general opposition to the sophists. It is to the credit of the Sophists that, as a consequence of their interest in truth and its grounding, especially in the moral and political spheres, they helped launch Western man into the life of reason. In Plato's judgment, that life, as they conducted it, lacked proper control, and reason's function of "cutting at the joints" of the real world was not achieved. The Sophists either relativized truth to particular, changeable circumstances, or denied the possibility of the attainment of truth, or made allowance for the presence of truth on both sides of an argument.

According to Plato, the truth about a question was determinate because the being about which any argument concerned itself was determinate (Rep. 478A480). Unreconciled opposition and irrational contradiction applied to appearances, not to the really intelligible; to opinion, not to knowledge. Truth dealt with the eternal, real unity over the many and changing appearances of it. In fact, man is able to organize the changing images of experience only to the extent that he can recognize the stable, intelligible models they reflect, just as one can organize various pictures of different people because he knows those who posed for them (ibid. 514A518).

Having this conviction about the character of truth and its object, Plato developed a method by which it became determinable. It was a method of approximation, and he traced out the various stages of approximation in a divided line of knowledge (ibid. 509E514). Truth is approached by stabilizing sense knowledge through postulated intelligible hypotheses. Through deduction from such hypotheses empirical knowledge is given a universality, necessity, and rational connection it does not have in itself. As merely postulated, however, hypotheses have no more justification than what the deduced empirical knowledge can afford them. Although modern empirical philosophers take this limitation as a virtue, Plato did not so regard it (ibid. 529A530).

To justify hypotheses requires the highest stage in knowledgedialectics (ibid. 511). As practiced by Plato, dialectics consist of a search for the unique meanings of the terms entering the hypothesis that make their synthesis as stated by the hypothesis necessary (ibid. 338C). Whatever is intelligibly necessary in this way must then be true, as the intelligible is the real and the real is the intelligible.

Discrimination of meanings for terms is not a conventional matter settled only by the pragmatic results for the user, as the Sophists would have it with their homo mensura doctrine. Any term taken in isolation signifies merely a mode in which the things man experiences can be alike. Before it has an unambiguous sense a mode of differing must be fixed with that likeness, since definition is by way of likeness and difference. Plato, however, held that the differences that can be thought along with any given likeness to obtain a definition is a matter of intelligibility itself, not merely of an operational success in practice. It is determined by a more comprehensive concept that can embrace both the given term and its contrary in its own meaning. Thinking the given term in the context of this more comprehensive concept fixes the mode of difference that can be thought along with it. This difference then consistently opposes its contrary and makes for an unambiguous discrimination in experience. A similar reconciliation of the comprehensive term with its contrary in a yet higher and richer term then becomes necessary.

Since things are determinately defined, and so have being, only as moments of an organically intelligible whole, the search in dialectics is for the ultimate whole that gives intelligibility and, therefore, being to all things. Dialectics culminates asymptotically in the vision of the good (ibid. 509A510). The success of the method is guaranteed because this ultimate comprehensive whole cannot be confused with anything else, since there is nothing more with which it can be confused. parmenides was basically right, except that the whole has an internal relational structure that makes rational discourse possible. Dialectics is the technique by which man explores this internal relational structure.

When Christian thinkers later speculated on revelation, seeking to give their faith an understanding, they found in platonism, with its notions of transcendence, imitation, and rational model for the world, a powerful ally (see dialectics in the middle ages).

Aristotle. With aristotle dialectics became a second-best method. This change in valuation is a consequence of his changed view about the real that is to be methodically explored. An intelligible is not stabilized as a transcendent form by its rational relations of sameness and difference to all other forms in one rational whole. It is stabilized by its being this way rather than not. For man's concepts express diverse modes of being, and not a common, formal mode above the many of experience. They express, moreover, not a transcendent mode above the many of experience but the diverse modes in which the many are.

The basic and diverse modes are Aristotle's catego ries of being. What man experiences is stabilized within a category by means of a difference specific to that mode of being and no other (see species). This difference, with the generic trait it specifies, is given to the thing by an efficient cause acting for some purpose; both genus and difference assume the role of definitory, actualizing form in relation to the thing's underlying matter (see matter and form). The mind's search is, therefore, for these definitory components as well as for the extrinsic causes responsible for the thing's coming under their determination, since all of these necessitate its being. Differences pertinent to another mode and their causes can be ignored since they are not necessary for the mode in question.

Repeated experience makes manifest differences that are specific; but once they are made manifest to the mind by experience, their connection with the categorical trait is then directly known. Such differences are recognized as a difference of one particular category and of no other, as being three-sided is immediately recognized as a mode of being a plane figure and not a mode of being a color. No dialectical search is required to fix these differences with a likeness, since the structure of being itself determines what differences make a difference and repeated experience of this stabilized structure leads to direct insight into it. Hypotheses are justified neither by dialectical search into meanings of terms, which could necessitate their synthesis in the hypothesis, nor by deduced empirical consequences, which could make them probably true. They are justified because the intellect intuitively recognizes that they state the causes of the thing, of that thing and no other, and that the thing could not, consequently, be other than it is (see causality).

Once specific differences and the causes responsible for their presence in the composite are discovered, they can be used as middle terms in arguments or syllogisms that show or demonstrate the necessity of the thing. Since such arguments proceed from middles that signify proper and constitutive causes, they are strictly scientific arguments (see demonstration).

Dialectical Reasoning. When the intellect, however, confronts an area of contingent beings or when it has not yet seized upon the proper and intrinsic causes of necessary things, it cannot argue scientifically. But, in Aristotle's view, inability to argue in this way does not mean complete inability to reason at all (Topica 100a 25101a 18). To be sure, any inferential process requires a middle term to join subject and predicate in the conclusion. But in lieu of the objective causes that show the objective necessity of their connection, a trace or sign of their connection can function as a middle for at least probable knowledge of their juncture. A sign cannot cause the being of the thing, but it can cause a probable knowledge of the thing. One such trace or sign of the thing's being is the logical order caused in the mind as it thinks about it. For Aristotle, the technique of establishing probable truth through a sign of this type is dialectical reasoning.

The problem of grounding the truth is not merely a question of looking to see whether things are the way one states them to be in propositions. Truths can be universal; and, therefore, some knowable principle must be used to establish them universally. In science this principle is the objective cause, which grounds the truth universally through the necessity it produces in the thing itself. In dialectics this principle is the kind of order of predicating universals that one can establish in his thought about things. For, in knowing, one knows universally and then relates universals to particulars in predication. Since the mode of predicating a universal is merely a logical order, it is impotent in the real. But since man's ability to predicate the universal according to a given mode is controlled by things, such predication can be taken as an intelligible sign of things. Being an intelligible sign involving a universal, it points to a connection in things that transcends, with some probability, the particulars immediately given in experience.

Because dialectics considers only the mode of predicating the universal and not the nature expressed in it, it is not limited to any one subject matter as is science (scientia ) in the strict sense (ibid. 104b 113). It becomes, therefore, a counterpart to rhetoricthe ability to persuade on almost any subject that is presented (Rhet. 1354a 15). The problem of rhetoric, however, is more complicated, since there it is not merely a question of establishing the probability of a belief, but of establishing it for a given audience. The principles that a rhetorician uses, accordingly, are not simply the commonplaces of dialectics, but also whatever is includable in argument that will dispose the audience to accept it. They include, therefore, his own character and the emotional dispositions of his audience as well.

Dialectical Problems. Ability to reason dialectically turns, in part, on a knowledge of the possible kinds of problems that can occur for a universal predicate is attributed to a subject, regardless of the peculiar natures they signify. Aristotle distinguishes four such problems based on a combination of convertibility with, and essentiality to, the subject. A universal predicated convertibly and essentially of the subject constitutes the problem of defini tion; predicated convertibly but not essentially, the dialectical problem of property; predicated essentially but not convertibly, the dialectical problem of genus; predicated nonessentially and nonconvertibly, the dialectical problem of accident (Topica 101b 1825, 101b 38102b 26, 103b 220).

An actual dialectical problem arises only when a universal is predicated of a subject in one of the above modes, not from the universal by itself. To ask, "Is 'an animal that walks on two feet' a definition of man or not?," raises a dialectical problem (ibid. 101b 2629). These problems form the subjects on which reasonings take place. If one changes the turn of the phrase and says, "'An animal that walks on two feet' is the definition of man, is it not?," he forms a dialectical proposition. These propositions are the materials with which arguments start; and since they differ from problems only in phraseology, they are equal in number to them. In either case, a grasp of the kinds of problems or propositions is requisite for dialectical skill.

Although a mode of predication accompanies every proposition and question, appeal to the mode of predication as a principle for grounding the truth is superfluous in those cases in which certainty is possible. Accordingly, not every proposition or every problem can be set down as dialectical. About things that are evident to everyone, no dialectical problem can be formed, since the truth about them is already known. Conversely, about things that no one would accept, no dialectical proposition can be formed, since they are evidently false (ibid. 104a 38). In dialectics the mind is dealing with the order it itself creates while judging about things. In evident things it does not advert to that order to make the judgment. In nonaccepted things no order is formed to which it could advert.

Techniques and Rules. Besides this formal knowledge of kinds of problems and propositions, dialectical skill, for its exercise, requires that one become well supplied with a stock of them. Aristotle organizes the acquisition of such a stock around four techniques: the securing of propositions; the distinction of senses of particular expressions; the discovery of the differences of things; and the investigation of their likenesses (ibid. 105a 2033). In the case of the last three, since it is always possible to make a proposition corresponding to each of them, one has techniques for securing propositions not yet formed, whereas the first systematically collects those already in existence.

In the discovering of the differences of things, care should be taken to preserve the dialectical character of the inquiry. If the things one examines are very far apart, the differences between them will be entirely obvious. No dialectical proposition is made about the obvious. A similar precaution should be observed with investigating likenesses. In things very close, the likeness is obvious. In securing propositions, they too should be selected in ways that correspond to distinctions drawn regarding their dialectical character. They should be about something having common agreement or the agreement of the experts. Since dialectics is not limited to any one objective subject matter, the propositions should further be organized according to their ethical, logical, or physical content. Distinction of meanings of terms can proceed also by the common dialectical technique of examining the senses of opposed terms. If the opposite has more than one sense, then the original has also (ibid. 105a 34108a 17).

With these techniques for supplying propositions and problems, it becomes possible to apply the commonplace rules that govern the four different modes of predication. Given the proposition "'animal' is the genus of man, is it not?," then "animal" should be true in every instance of man, applicable to other things as well, and predicated in the same category as "man." It would be possible to defend the proposition by showing that everyone agrees or that the experts agree in applying the term universally to men; that, in cases in which it is denied of man, the sense of the term that is denied is different from its asserted sense; that men are like tigers, which are conceded to be animals; or that men are radically different from the things an opponent would allege as constituting the class to which men belong. Most of Aristotle's treatise on dialectics is given over to delineating these commonplace rules for each of the modes of predication.

The value of dialectics becomes apparent from its nature (ibid. 101a 25101b 4). That it is useful as an intellectual training follows from the orderly plan of inquiry based on the modes of predication one is able to bring to bear on a subject; he is thus able to argue more easily about it. It also has a value in disputes with people on contingent matters. One can meet them on commonly accepted grounds or oppose them with authorities more expert than the ones they cite. In regard to matters necessary in themselves, but for which one does not yet know the proximate principles of the scientific proof, it disposes the mind to those principles by establishing the facts for which they must account. The more one can establish as probably true of a subject, the better his chances of inducing the indemonstrable premise from which genuine science can start. Finally, it defends the principles themselves when they come under attack. Principles cannot be scientifically proved, being the condition for all proof in a field; they can only be dialectically defended.

Moderns. Science, as that term is understood in modern thought, does not search for causes in the sense in which Aristotle deemed necessary for certain knowledge of the world. Hence, his account of the general nature of scientific method does not generally receive a favorable hearing. Modern investigators into nature are content to discover and confirm empirical hypotheses that merely give a probable rule for the anticipation of future experience [A. J. Ayer, Language, Truth and Logic (2d ed. London 1946) 41]. Empirical hypotheses, however, have two dimensions to them: a formal structure supplied by the scientist's logical system and a material content supplied by experience. Empirical confirmation, through examination of likenesses and differences, of one's ability to think the data in the formal mode of organization given to them by the hypothesis is then taken as an indication of the probable truth of the hypothesis. The procedure is much like what Aristotle would call dialectics. Although the Aristotelian logical modes of definition, genus, property, and accident are not explicitly in the forefront of discussion of logical frameworks (being based on the subject-predicate formal relation), the dialectical techniques for accumulating a supply of problems and propositions and for applying the commonplace rules of whatever logical modes are used are still valued. Consensus of the experts, distinction in meanings of terms, and discovery of likenesses and differences are still carried on, albeit at a more sophisticated level.

Modern theoreticians of science are also inclined to classify problems on the basis of the subject dealt with, in the dialectical fashion that Aristotle recognized. Problems of determining the formal structure of hypotheses are logical problems; those dealing with the predictable empirical content of hypotheses are problems of physics in the broad sense; and those dealing with emotional expression relative to what one experiences are ethical problems. Although Aristotle recognized such a dialectical division of problems, he complemented it with a scientific division into theoretical, practical, and productive.

In the history of philosophy subsequent to Aristotle's time, dialectics has often been elevated, as with Plato, to the primary method for examining the real. The character of the real and the character of the principles by which the dialectical method can be brought to bear on the real have not, however, been the same as Plato's. At times the method is conceived on an idealist base, as with G. W.F. hegel, in which, through the dialectical process, Spirit reflexively realizes itself in ever more encompassing totalities (see hegelianism and neo-hegelianism). At others, it is conceived on a materialist base, as with K. marx, in which, through the dialectical process, man actionally overcomes class antagonisms in ameliorating his social world into a classless society. Dialectics is calculated, however, to reconcile just such oppositions as that between spirit and matter (see materialism, dialectical and historical).

See Also: argumentation; methodology (philosophy); reasoning.

Bibliography: m. j. adler, Dialectic (New York 1927). m. j. adler, ed. The Great Ideas: A Syntopicon of Great Books of the Western World, 2 v. (Chicago 1952) 1:345357. c. capone braga, Enciclopedia filosofica, 4 v. (Venice-Rome 1957) 1:15391559, complete bibliog.; Della dialettica (Turin 1953). r. eisler, Wörterbuch der philosophischen Begriffe, 3 v. (4th ed. Berlin 192730) 1:268272. t. gilby, Barbara Celarent: A Description of Scholastic Dialectic (New York 1949). l. m. rÈgis, L'Opinion selon Aristote (Ottawa 1935). b. lakebrink, Hegels dialektische Ontologie und die Thomistische Analektik (Cologne 1955).

[j. j. ziegler]