(4) But this science, this Dialectic essential to all the three classes alike, what, in sum, is it?

It is the Method, or Discipline, that brings with it the power of pronouncing with final truth upon the nature and relation of things- what each is, how it differs from others, what common quality all have, to what Kind each belongs and in what rank each stands in its Kind and whether its Being is Real-Being, and how many Beings there are, and how many non-Beings to be distinguished from Beings.

Dialectic treats also of the Good and the not-Good, and of the particulars that fall under each, and of what is the Eternal and what the not Eternal- and of these, it must be understood, not by seeming-knowledge but with authentic science.

All this accomplished, it gives up its touring of the realm of sense and settles down in the Intellectual Kosmos and there plies its own peculiar Act: it has abandoned all the realm of deceit and falsity, and pastures the Soul in the "Meadows of Truth": it employs the Platonic division to the discernment of the Ideal-Forms, of the Authentic-Existence and of the First-Kinds : it establishes, in the light of Intellection, the unity there is in all that issues from these Firsts, until it has traversed the entire Intellectual Realm: then, resolving the unity into the particulars once more, it returns to the point from which it starts.

Now rests: instructed and satisfied as to the Being in that sphere, it is no longer busy about many things: it has arrived at Unity and it contemplates: it leaves to another science all that coil of premisses and conclusions called the art of reasoning, much as it leaves the art of writing: some of the matter of logic, no doubt, it considers necessary- to clear the ground- but it makes itself the judge, here as in everything else; where it sees use, it uses; anything it finds superfluous, it leaves to whatever department of learning or practice may turn that matter to account.

(10) Another method of division is possible: substances may be classed as hot-dry, dry-cold, cold-moist, or however we choose to make the coupling. We may then proceed to the combination and blending of these couples, either halting at that point and going no further than the compound, or else subdividing by habitation- on the earth, in the earth- or by form and by the differences exhibited by living beings, not qua living, but in their bodies viewed as instruments of life.

Differentiation by form or shape is no more out of place than a division based on qualities- heat, cold and the like. If it be objected that qualities go to make bodies what they are, then, we reply, so do blendings, colours, shapes. Since our discussion is concerned with Sensible Substance, it is not strange that it should turn upon distinctions related to sense-perception: this Substance is not Being pure and simple, but the Sensible Being which we call the Universe.

We have remarked that its apparent subsistence is in fact an assemblage of Sensibles, their existence guaranteed to us by sense-perception. But since their combination is unlimited, our division must be guided by the Form-Ideas of living beings, as for example the Form-Idea of Man implanted in Body; the particular Form acts as a qualification of Body, but there is nothing unreasonable in using qualities as a basis of division.

We may be told that we have distinguished between simple and composite bodies, even ranking them as opposites. But our distinction, we reply, was between material and organic bodies and raised no question of the composite. In fact, there exists no means of opposing the composite to the simple; it is necessary to determine the simples in the first stage of division, and then, combining them on the basis of a distinct underlying principle, to differentiate the composites in virtue of their places and shapes, distinguishing for example the heavenly from the earthly.

These observations will suffice for the Being , or rather the Becoming, which obtains in the Sensible realm.

(2) Now the reasoning faculty which undertakes this problem is not a unity but a thing of parts; it brings the bodily nature into the enquiry, borrowing its principles from the corporeal: thus it thinks of the Essential Existence as corporeal and as a thing of parts; it baulks at the unity because it does not start from the appropriate principles. We, however, must be careful to bring the appropriately convincing principles to the discussion of the Unity, of perfect Being: we must hold to the Intellectual principles which alone apply to the Intellectual Order and to Real Being.

On the one hand there is the unstable, exposed to all sorts of change, distributed in place, not so much Being as Becoming: on the other, there is that which exists eternally, not divided, subject to no change of state, neither coming into being nor falling from it, set in no region or place or support, emerging from nowhere, entering into nothing, fast within itself.

In dealing with that lower order we would reason from its own nature and the characteristics it exhibits; thus, on a plausible foundation, we achieve plausible results by a plausible system of deduction: similarly, in dealing with the Intellectual, the only way is to grasp the nature of the essence concerned and so lay the sure foundations of the argument, not forgetfully straying over into that other order but basing our treatment on what is essential to the Nature with which we deal.

In every entity the essential nature is the governing principle and, as we are told, a sound definition brings to light many even of the concomitants: where the essential nature is the entire being, we must be all the more careful to keep to that, to look to that, to refer all to that.

(18) These problems at any rate all serve to show that, while in general it is necessary to look for differences by which to separate things from each other, to hunt for differences of the differences themselves is both futile and irrational. We cannot have substances of substances, quantities of quantities, qualities of qualities, differences of differences; differences must, where possible, be found outside the genus, in creative powers and the like: but where no such criteria are present, as in distinguishing dark-green from pale-green, both being regarded as derived from white and black, what expedient may be suggested?

Sense-perception and intelligence may be trusted to indicate diversity but not to explain it: explanation is outside the province of sense-perception, whose function is merely to produce a variety of information; while, as for intelligence, it works exclusively with intuitions and never resorts to explanations to justify them; there is in the movements of intelligence a diversity which separates one object from another, making further differentiation unnecessary.

Do all qualities constitute differentiae, or not? Granted that whiteness and colours in general and the qualities dependent upon touch and taste can, even while they remain species , become differentiae of other things, how can grammar and music serve as differentiae? Perhaps in the sense that minds may be distinguished as grammatical and musical, especially if the qualities are innate, in which case they do become specific differentiae.

It remains to decide whether there can be any differentia derived from the genus to which the differentiated thing belongs, or whether it must of necessity belong to another genus? The former alternative would produce differentiae of things derived from the same genus as the differentiae themselves- for example, qualities of qualities. Virtue and vice are two states differing in quality: the states are qualities, and their differentiae qualities- unless indeed it be maintained that the state undifferentiated is not a quality, that the differentia creates the quality.

But consider the sweet as beneficial, the bitter as injurious: then bitter and sweet are distinguished, not by Quality, but by Relation. We might also be disposed to identify the sweet with the thick, and the Pungent with the thin: "thick" however hardly reveals the essence but merely the cause of sweetness- an argument which applies equally to pungency.

We must therefore reflect whether it may be taken as an invariable rule that Quality is never a differentia of Quality, any more than Substance is a differentia of Substance, or Quantity of Quantity.

Surely, it may be interposed, five differs from three by two. No: it exceeds it by two; we do not say that it differs: how could it differ by a "two" in the "three"? We may add that neither can Motion differ from Motion by Motion. There is, in short, no parallel in any of the other genera.

In the case of virtue and vice, whole must be compared with whole, and the differentiation conducted on this basis. As for the differentia being derived from the same genus as themselves, namely, Quality, and from no other genus, if we proceed on the principle that virtue is bound up with pleasure, vice with lust, virtue again with the acquisition of food, vice with idle extravagance, and accept these definitions as satisfactory, then clearly we have, here too, differentiae which are not qualities.

(13) It has been remarked that the continuous is effectually distinguished from the discrete by their possessing the one a common, the other a separate, limit.

The same principle gives rise to the numerical distinction between odd and even; and it holds good that if there are differentiae found in both contraries, they are either to be abandoned to the objects numbered, or else to be considered as differentiae of the abstract numbers, and not of the numbers manifested in the sensible objects. If the numbers are logically separable from the objects, that is no reason why we should not think of them as sharing the same differentiae.

But how are we to differentiate the continuous, comprising as it does line, surface and solid? The line may be rated as of one dimension, the surface as of two dimensions, the solid as of three, if we are only making a calculation and do not suppose that we are dividing the continuous into its species; for it is an invariable rule that numbers, thus grouped as prior and posterior, cannot be brought into a common genus; there is no common basis in first, second and third dimensions. Yet there is a sense in which they would appear to be equal- namely, as pure measures of Quantity: of higher and lower dimensions, they are not however more or less quantitative.

Numbers have similarly a common property in their being numbers all; and the truth may well be, not that One creates two, and two creates three, but that all have a common source.

Suppose, however, that they are not derived from any source whatever, but merely exist; we at any rate conceive them as being derived, and so may be assumed to regard the smaller as taking priority over the greater: yet, even so, by the mere fact of their being numbers they are reducible to a single type.

What applies to numbers is equally true of magnitudes; though here we have to distinguish between line, surface and solid- the last also referred to as "body"- in the ground that, while all are magnitudes, they differ specifically.

It remains to enquire whether these species are themselves to be divided: the line into straight, circular, spiral; the surface into rectilinear and circular figures; the solid into the various solid figures- sphere and polyhedANSWER: whether these last should be subdivided, as by the geometers, into those contained by triangular and quadrilateral planes: and whether a further division of the latter should be performed.

(5) But whence does this science derive its own initial laws?

The Intellectual-Principle furnishes standards, the most certain for any soul that is able to apply them. What else is necessary, Dialectic puts together for itself, combining and dividing, until it has reached perfect Intellection. "For," we read, "it is the purest of Intellection and Contemplative-Wisdom." And, being the noblest method and science that exists it must needs deal with Authentic-Existence, The Highest there is: as Contemplative-Wisdom it deals with Being, as Intellection with what transcends Being.

What, then, is Philosophy?

Philosophy is the supremely precious.

Is Dialectic, then, the same as Philosophy?

It is the precious part of Philosophy. We must not think of it as the mere tool of the metaphysician: Dialectic does not consist of bare theories and rules: it deals with verities; Existences are, as it were, Matter to it, or at least it proceeds methodically towards Existences, and possesses itself, at the one step, of the notions and of the realities.

Untruth and sophism it knows, not directly, not of its own nature, but merely as something produced outside itself, something which it recognises to be foreign to the verities laid up in itself; in the falsity presented to it, it perceives a clash with its own canon of truth. Dialectic, that is to say, has no knowledge of propositions- collections of words- but it knows the truth, and, in that knowledge, knows what the schools call their propositions: it knows above all, the operation of the soul, and, by virtue of this knowing, it knows, too, what is affirmed and what is denied, whether the denial is of what was asserted or of something else, and whether propositions agree or differ; all that is submitted to it, it attacks with the directness of sense-perception and it leaves petty precisions of process to what other science may care for such exercises.