The way in which logical doctrine is developed in the Aristo telian treatises fits in with this view. Doubtless what we have is in the main a reflex of the heuristic character of Aristotle's own work as pioneer. But it at least satisfies the requirement that the enquiry shall carry the plain man along with it. Actual modes of expression are shown to embody distinctions which average intelligence can easily recognize, and will readily ac knowledge, though they may tend by progressive rectification fun damentally to modify the assumption natural to the level of thought from which he begins. Thus we start from the point of view of a world of separate persons and things, in which thought mirrors these concrete realities, taken as ultimate subjects of predicates. It is a world of communication of thought, where per sons as thinkers need to utter in language truths objectively valid for the common world. In these truths predicates are accepted or rejected by subjects, and therefore depend on the reflection of fact in proposition. These are combinatory of parts, attaching or detaching predicates, and so involving subject, predi cate and copula. At this stage we are as much concerned with speech-forms as the thought-forms of which they are conven tional symbols, with Plato's analysis, for instance, into a noun and a verb, whose connotation of time is as yet a difficulty. The universal of this stage is the universal of fact, what is recognized as predicable of a plurality of subjects. The dialectical doctrine of judgment as the declaration of one member of a disjunction by contradiction, which is later so important, is struggling with one of its initial difficulties, viz., the contingency of particular events, the future solution of which remains imperfect.
The doctrine of the Categories is still on the same level of thought, though its grammatico-logical analysis is the more ad vanced one which had probably been developed by the Academy before Aristotle came to think of his friends there as "them" rather than "us." It is what in one direction gave the now familiar classification of parts of speech, in the other that of thought categories underlying them. If we abstract from any actual com bination of subject and predicate and proceed to determine the types of predicate asserted in simple propositions of fact, we have on the one hand a subject which is never object, a "first sub stance" or concrete thing, of which may be predicated in the first place, "second substance," expressing that it is a member of a concrete class, and in the second place quantity, quality, correla tion, action and the like. The list follows the forms of the Greek language so closely that a category emerges appropriated to the use of the perfect tense of the middle voice to express the relation of the subject to a garb that it dons. In all this the individual is the sole self-subsistent reality. Truth and error are about the individual and attach or detach predicates correctly and incor rectly. There is no committal to the metaphysics in the light of which the logical enquiry is at last to find its complete justifica tion. The point of view is to be modified profoundly by what follows—by the doctrine of the class-concept behind the class, of the form or idea as the constitutive formula of a substance, or, again, by the requirement that an essential attribute must be grounded in the nature or essence of the substance of which it is predicated, and that such attributes alone are admissible predi cates from the point of view of the strict ideal of science. But we are still on the ground of common opinion, and these doctrines are not yet laid down as fundamental to the development.
Dialectic, then, though it may prove to be the ultimate method of establishing principles in philosophy, starts from the probable and conceded premises, and deals with them only in the light of common principles, such as may be reasonably appealed to or easily established against challenge. To the expert, in any study which involves contingent matter, i.e., an irreducible element of indetermination, e.g., to the physician, there is a specific form of this, but the reflection that this is so is something of an after thought. We start with what is prima facie given, to return upon it from the ground of principles clarified by the sifting process of dialectic and certified by thought. The Topics deal with dia lectic and constitute an anatomy of argumentation, or, according to what seems to be Aristotle's own metaphor, a survey of the tactical vantage-points (7-67rot) for the conflict of wits in which the prize is primarily victory, though it is a barren victory unless it is also knowledge. It is in this treatise that what have been called "the conceptual categories" emerge, viz., the predicables, or heads of predication as it is analysed in relation to the pro visional theory of definition that dialectic allows and requires. A predicate either is expressive of the essence or part of the essence of the subject, viz., that original group of mutually underivable attributes of which the absence of any one destroys its right to the class-name, or it is not. Either it is convertible with the subject or it is not. Here, then, judgment, though still viewed as combinatory, has the types which belong to coherent systems of implication discriminated from those that predicate coincidence or accident, i.e., any happening not even derivatively essential from the point of view of the grouping in which the subject has found a place. In the theory of dialectic any predicate may be suggested for a subject, and if not affirmed of it, must be denied of it, if not denied must be affirmed. The development of a theory of the ground on which subjects claim their predicates and disown alien predicates could not long be postponed. In practical dia lectic the unlimited possibility was reduced to manageable pro portions in virtue of the groundwork of received opinion upon which the operation proceeded. It is in the Topics, further, that we clearly have a first treatment of syllogism as formal implica tion, with the suggestion that advance must be made to a view of its use for material implication from true and necessary prin ciples. It is in the Topics, again, that we have hints at the devices of an inductive process, which, as dialectical, throw the burden of producing contradictory instances upon the other party to the discussion. In virtue of the common-stock of opinion among the interlocutors, and their potentially controlling audience, this process was more valuable than appears on the face of things. Obviously tentative, and with limits and ultimate interpretation to be determined elsewhere, it failed to bear fruit till the Renais sance, and then by the irony of fate to the discrediting of Aris totle. In any case, however, definition, syllogism, induction all invited further determination, especially if they were to take their place in a doctrine of truth or knowledge. The problem of ana lytic, i.e., of the resolution of the various forms of inference into their equivalents in that grouping of terms or premises which was most obviously cogent, was a legacy of the Topics. The debate game had sought for diversion and found truth, and truth raised the logical problem on a different plane.