PROPOSITION XLIX.

To sensile perception, Matter, as determined by Quantity that is definite in measure and shape, and that, consequently, presupposes the complete constitution of the substantial Composite, is the principle by which material Substances are individuated.

This Proposition has been added, in order to make the statement of St. Thomas's teaching on this subject of Individuation complete; otherwise, it would find a more fitting place in Ideology than in Metaphysics. The proof will naturally assume the form of a declaration, rather than of a demonstration. No one can doubt but that what are called, in the Peripatetic Philosophy, Accidents, -- such as, shape, colour, warmth, hardness, and the like, -- are the formal objects of the senses. We cannot see, hear, smell, taste, Matter in itself; a fortiori, the senses cannot directly perceive the substantial Form. The whole Substance of material things is out of sight, and is shrouded in a panorama of Accidents. Nay, more; the action of purely material Substances (all that is, save man) is not immediate; they energize, only through their Accidents, as by necessary instruments. The adequate formal object, therefore, of the senses, are the Accidents of material things; for it is the province of the Intellect alone to contemplate Natures, or Essences. Consequently, it is obvious that sensile perception of the Individual, as such, must be founded in Accidental differences; or it can have no foundation at all. And, as a fact, men do distinguish individual material substances in this way. How is it that one distinguishes this piece of coal from that; save that each is under the defined limits of its own Quantity, which give to it its shape? So, the herdsman knows his cattle one from the other, by spots, colour of the body or legs, form of the head, bend of the horn, or some such accidental differences. In like manner, one man is sensilely distinguished from another by his height, size, features, proportion of limbs, all of which belong to the qualities of Quantity; or by the colour of his hair, eyes, skin, which are simply included in the Category of Quality. The Comedy of Errors reminds us what confusion may arise when two persons are so exactly alike, as to exhibit no special notes of distinction. It is further worthy of remark, that to the perception of sense, the Accidents individuate each other, so to say, in their mutual transcendental relation. Thus, -- to resume one of the illustrations just given, -- the shape, or quantitative limits, of the lump of coal would not be recognized by the sight, if it were not for the blackness which informs the mass; while the blackness would be indefinite and, consequently, disappear for want of contrast, unless it were limited and defined by Quantity. After a like manner, in the case of a blind man, hardness, softness, roughness, or polish of surface, would serve to define the Quantity; and the Quantity, in turn, would supply the limit to his touch. This might reasonably be expected; since, as Quantity determines and distinguishes Matter, so Quality determines and distinguishes Quantity. Let it not, however, be supposed, that these accidental determinations constitute the individuant, or individualizing, differentia of material Substances. They are the effect of the Haecceity of such substance, not its cause; though, to sensile perception, they are truly differential.

It only remains to add a caution. Be on your guard against confounding Individuation, or Haecceity, with Identity. Identity is a persevering sameness of the Individual. This is one principal reason why St. Thomas, whenever he treats of the sensile perception of the Individual, introduces determination of place and time; whilst he excludes determinate Quantity, whether as determined by its own limits or by qualitative Forms, from the metaphysical constitution of individual Substance. For a man may be at one time two feet high; at another, over six feet. At one time he may be thin; later on, fat, In the course of years, his features, the colour of his hair, etc., materially change. So again, when he was in England, he had a fair complexion; since living in India, he has become sallow or brown. But, evidently, if it is a question of purely sensile perception, a man will be recognized as this individual, and distinguishable from every other, by his appearance hic et nunc; not by what he may become some thirty years hence. It is precisely for the same reason, that these determined dimensions must not be allowed an entrance into the Metaphysical, or Essential, constitution of Haecceity; otherwise, as St. Thomas sagely remarks, as often as a man grows in height or bulk, or changes in appearance, -- as when does he not? -- he would cease to be himself, and commence to be somebody else, in an endless succession. And now for St. Thomas. Passages, already quoted in the preceding Proposition, have indicated with sufficient clearness the teaching of the Angelic Doctor on this head. Nevertheless, one other passage shall be presented to the reader, in which he expresses himself in very explicit terms. These are his words: 'But it' (i.e. individual material Substance) 'does not become hic et nunc apparent, without determinate and fixed dimensions, which it must necessarily have, from the fact that the Form is received in Matter; since it is impossible for it to be received in Matter, without the constitution thereby of a corporal Substance, under whose special shape or figure such dimensions are included. Wherefore, it is said that Matter, under fixed dimensions, is the cause of Individuation. Not that the dimensions are the cause of the Individual, -- since an Accident does not cause its own Subject; but, because it is made hic et nunc apparent by fixed dimensions, as by a peculiar and inseparable sign of the Individual.'^{1}

{1} 'Sed non fit hic et nunc demonstrabile sine dimensionibus determinatis et certis, quas habere necesse est, eo quod forma recipitur in materia: cum impossibile sit eam recipi in materia, qua constituatur corpus substantiae, sub cujus propria figura sunt dimensiones ipsae. Et ideo dicitur quod materia sub certis dimensionibus est causa individuationis. Non quod dimensiones causent individuum; cum accidens non causet suum subjectum; sed quia per dimensiones certas demonstratur individuum hic et nunc, sicut per signum proprium individui et inseparabile.' Opusc. XXXII (aliter XX VIII), De natura materiae et dimensionibus interminatis, c. 3, in fi. For the fuller comprehension of this passage, the reader is referred back to a quotation made from the same treatise in the first member of Proposition xlviii, of which the words here cited are the immediate continuation.