But we have still to explain combination, for that was the third of the subjects we originally proposed to discuss. Our explanation will proceed on the same method as before. We must inquire: What is combination, and what is that which can combine? Of what things, and under what conditions, is combination a property? And, further, does combination exist in fact, or is it false to assert its existence?
For, according to some thinkers, it is impossible for one thing to be combined with another. They argue that (i) if both the combined constituents persist unaltered, they are no more combined now than they were before, but are in the same condition: while (ii) if one has been destroyed, the constituents have not been combined--on the contrary, one constituent is and the other is not, whereas combination demands uniformity of condition in them both: and on the same principle (iii) even if both the combining constituents have been destroyed as the result of their coalescence, they cannot have been combined since they have no being at all.
What we have in this argument is, it would seem, a demand for the precise distinction of combination from coming-to-be and passing-away (for it is obvious that combination, if it exists, must differ from these processes) and for the precise distinction of the combinable from that which is such as to come-to-be and pass-away. As soon, therefore, as these distinctions are clear, the difficulties raised by the argument would be solved.
Now (i) we do not speak of the wood as combined with the fire, nor of its burning as a combining either of its particles with one another or of itself with the fire: what we say is that the fire is coming-to-be, but the wood is passing-away. Similarly, we speak neither (ii) of the food as combining with the body, nor (iii) of the shape as combining with the wax and thus fashioning the lump. Nor can body combine with white, nor (to generalize) properties and states with things: for we see them persisting unaltered. But again (iv) white and knowledge cannot be combined either, nor any other of the adjectivals. (Indeed, this is a blemish in the theory of those who assert that once upon a time all things were together and combined. For not everything can combine with everything. On the contrary, both of the constituents that are combined in the compound must originally have existed in separation: but no property can have separate existence.)
Since, however, some things are-potentially while others are-actually, the constituents combined in a compound can be in a sense and yet not-be. The compound may he-actually other than the constituents from which it has resulted; nevertheless each of them may still he-potentially what it was before they were combined, and both of them may survive undestroyed. (For this was the difficulty that emerged in the previous argument: and it is evident that the combining constituents not only coalesce, having formerly existed in separation, but also can again be separated out from the compound.) The constituents, therefore, neither (a) persist actually, as body and white persist: nor (b) are they destroyed (either one of them or both), for their power of action is preserved. Hence these difficulties may be dismissed: but the problem immediately connected with them-whether combination is something relative to perception must be set out and discussed.
When the combining constituents have been divided into parts so small, and have been juxtaposed in such a manner, that perception fails to discriminate them one from another, have they then been combined Or ought we to say No, not until any and every part of one constituent is juxtaposed to a part of the other? The term, no doubt, is applied in the former sense: we speak, e.g. of wheat having been combined with barley when each grain of the one is juxtaposed to a grain of the other. But every body is divisible and therefore, since body combined with body is uniform in texture throughout, any and every part of each constituent ought to be juxtaposed to a part of the other.
No body, however, can be divided into its least parts: and composition is not identical with combination, but other than it. From these premises it clearly follows (i) that so long as the constituents are preserved in small particles, we must not speak of them as combined. (For this will be a composition instead of a blending or combination: nor will every portion of the resultant exhibit the same ratio between its constituents as the whole. But we maintain that, if combination has taken place, the compound must be uniform in texture throughout-any part of such a compound being the same as the whole, just as any part of water is water: whereas, if combination is composition of the small particles, nothing of the kind will happen. On the contrary, the constituents will only be combined relatively to perception: and the same thing will be combined to one percipient, if his sight is not sharp, (but not to another,) while to the eye of Lynceus nothing will be combined.) It clearly follows (ii) that we must not speak of the constituents as combined in virtue of a division such that any and every part of each is juxtaposed to a part of the other: for it is impossible for them to be thus divided. Either, then, there is no combination, or we have still to explain the manner in which it can take place.
Now, as we maintain, some things are such as to act and others such as to suffer action from them. Moreover, some things-viz. those Which have the same matter-reciprocate, i.e. are such as to act upon one another and to suffer action from one another; while other things, viz. agents which have not the same matter as their patients, act without themselves suffering action. Such agents cannot combine-that is why neither the art of healing nor health produces health by combining with the bodies of the patients. Amongst those things, however, which are reciprocally active and passive, some are easily-divisible. Now (i) if a great quantity (or a large bulk) of one of these easily-divisible reciprocating materials be brought together with a little (or with a small piece) of another, the effect produced is not combination, but increase of the dominant: for the other material is transformed into the dominant. (That is why a drop of wine does not combine with ten thousand gallons of water: for its form is dissolved, and it is changed so as to merge in the total volume of water.) On the other hand (ii) when there is a certain equilibrium between their powers of action, then each of them changes out of its own nature towards the dominant: yet neither becomes the other, but both become an intermediate with properties common to both.
Thus it is clear that only those agents are combinable which involve a contrariety-for these are such as to suffer action reciprocally. And, further, they combine more freely if small pieces of each of them are juxtaposed. For in that condition they change one another more easily and more quickly; whereas this effect takes a long time when agent and patient are present in bulk.
Hence, amongst the divisible susceptible materials, those whose shape is readily adaptable have a tendency to combine: for they are easily divided into small particles, since that is precisely what being readily adaptable in shape implies. For instance, liquids are the most combinable of all bodies-because, of all divisible materials, the liquid is most readily adaptable in shape, unless it be viscous. Viscous liquids, it is true, produce no effect except to increase the volume and bulk. But when one of the constituents is alone susceptible-or superlatively susceptible, the other being susceptible in a very slight degree-the compound resulting from their combination is either no greater in volume or only a little greater. This is what happens when tin is combined with bronze. For some things display a hesitating and ambiguous attitude towards one another-showing a slight tendency to combine and also an inclination to behave as receptive matter and form respectively. The behaviour of these metals is a case in point. For the tin almost vanishes, behaving as if it were an immaterial property of the bronze: having been combined, it disappears, leaving no trace except the colour it has imparted to the bronze. The same phenomenon occurs in other instances too.
It is clear, then, from the foregoing account, that combination occurs, what it is, to what it is due, and what kind of thing is combinable. The phenomenon depends upon the fact that some things are such as to be (a) reciprocally susceptible and (b) readily adaptable in shape, i.e. easily divisible. For such things can be combined without its being necessary either that they should have been destroyed or that they should survive absolutely unaltered: and their combination need not be a composition, nor merely relative to perception. On the contrary: anything is combinable which, being readily adaptable in shape, is such as to suffer action and to act; and it is combinable with another thing similarly characterized (for the combinable is relative to the combinable); and combination is unification of the combinables, resulting from their alteration.