​Note 1, p. 11. Truth in relation to nature, &c.] Aristotle^[1] says that some beings exist by nature, and some by other causes; those by nature include animals and their parts, plants and elementary bodies, as fire and air, earth and water, for all such, evidently, exist, and exist by nature. The objects, in fact, of nature's constitution are broadly distinguished from whatever does not emanate from her—"for all her productions appear to have within them a principle of motion, and of rest; some for locomotion, and some for the motions of growth, decay, and change. But neither a bed, a garment, nor any other similar object, whether formed of stone, earth, or composition, has any such innate tendency to change; and thus nature is to be regarded as the source and first cause of motion and rest in something which has, not casually but, innately, in itself, from its origin, the capability of being so acted upon." The term nature^[2], besides, is applied to any substance which, however rude and unchangeable, admits, by its own properties, of being converted into something, as ​bronze is said to be the nature of a statue or of bronze utensils, wood of wooden articles, and so of other materials and products. There were some who spoke of the essence of natural bodies as nature, and as they made the primal combination of particles, that is affinity, to be essence, Empedocles maintained that "the nature spoken of by men is only the combination of and change among particles." So that Aristotle confined the term nature to existing beings and the processes by which they are supported and perpetuated, to living and organised matter that is, while others widened its acceptation, and made it applicable to the changes continually going on through and by elementary substances. With him, in fact, it was a living principle; with others, a property or force, whereby change is a law.

"The term nature," says Cuvier^[3], "in our own and most other tongues, signifies, sometimes the properties which a being derives from its birth (hereditarily) in contradistinction to those which it may derive from adventitious circumstances; sometimes the whole of the beings which compose the universe, and sometimes, again, the laws to which those beings are subjected. It is in this last sense that we are accustomed to personify nature, and out of respect to employ its name for that of its author."

Note 2, p. 11. Its essence as well as its accidents.] Aristotle^[4] observes that essence seems, most manifestly, ​to be an innate property in bodies; and, therefore, animals and plants, and parts of animals and plants, as well as natural bodies, as fire and water, air and earth, the elements, in fact, are essences; to which may be added the bodies which are derived from the elements, as the heavens, stars, sun, and moon. Some, however, regarded the boundaries of bodies, as surface, line, point, and unit, as essences, rather than bodies or solids themselves. Thus, essence, according to the first definition, seems to be scarcely distinguishable from nature. Aristotle^[5], however, in another passage, considers it under four heads: as mode of being, as universal, genus, and subject; and subject he held to be essence in a fuller sense than the others. Plato admitted of essence in forms, mathematical abstractions, as also in sentient bodies; and the Pythagoreans first, and Plato later, adopted unity as essence. Aristotle, in fact, seems to confine his definitions of these abstract powers or entities to the outer world; and others to comprehend, under the term, the abstractions of pure science, and the immediate operations of general laws.

The term "accident" was with Aristotle^[6], as it is with us, significant of chance or possibility, as well as what is necessary and constant. The former is exemplified by an individual, when digging, finding a treasure, as this is an occurrence neither necessary nor constant; and thus there can be no assignable cause, save chance, which itself is undefinable, he adds, for an incident so purely casual. ​But it also implies properties which, although not essential, are, still, inherent, inalienable from, and distinctive of particular bodies, as it is a property of the triangle to contain two right angles; these properties only are regarded as accidents in modern science, and such are implied in the passage alluded to.

Note 3, p. 12. Concerning the thing itself, &c.] This stands first in the enumeration of the categories^[7], which comprize the ten following—thing itself; (τί ἐστι); quantity; quality; relation; when; where; position; recipiency; action; and impression. They are so designated, Aristotle says, because there must ever be, in some one of them, accident and genus, individual, and definition; for it is through them that premisses signify either individual, or quantity, or quality, or other one of those enumerated. It is made evident, thus—when it is said of a man lying down that it is a man or an animal, the party both says what it is, and points out its essence; when it is something white which is lying down, then the party designates its quality, as well. But these two exemplifications seem to shew that the terms essence, accidents, category, like the abstractions of which they are the representatives, cannot be clearly distinguished from one another; so that they may almost be regarded as derivatives from one comprehensive idea. Essence is, in the first of those instances, almost confounded with the categories, although it is the object^[8] of a special inquiry; ​and this seeming incongruity may have led some scholars to set it down among them.

Note 4, p. 12. Some kind of demonstration or division, &c.] Demonstration is, according to Aristotle^[9], a scientific syllogism, and by scientific is meant, he says, the method, through which we learn, with certainty, what a subject may be; and, if the knowledge be such, it follows that demonstrative knowledge must be derived from conditions which are original, immediate, and more apprehensible and causative, than the conclusion sought for. Those conditions are, in fact, the suitable principles for ascertaining that which is to be demonstrated; as, without them, the result will be, not demonstration but, a syllogism, which cannot, with certainty, eliminate truth. Thus, while demonstration^[10] is a kind of syllogism, every syllogism is not demonstration. Division is said by Aristotle^[11]to be an imperfect syllogism, for it assumes what ought to

be demonstrated, and draws conclusions from à priori reasonings. In this allusion to division, Aristotle may be supposed to have had Plato in view, "as it was by a process of dividing and subdividing that that eminent man conducted his inquiries after truth;" as, however, this method was considered by him to be a faulty or imperfect syllogism, it may be that he alluded to it as one which might be adopted, without altogether approving of it as a mental process. ​

Note 5, p. 12. As those of number are not those of plane surfaces, &c.] That is, the science of number differs, generically, from that of Geometry. The nature, so to say, of numbers had been a subject of deep and curious speculation long before and during the age of Aristotle, and there lie scattered through his works notices of writers and systems which, although in themselves interesting to scholars, would, even were it possible to give a clear summary of them, be foreign to the present inquiry. Aristotle^[12], before entering upon number, defined "quantity" as being, partly definite, and partly continuous—and the former he constituted of parts which have no mutual local relation to each other; the latter of parts which have that relation. The "definite" quantity is represented "by number and by a word; the continuous by line, surface, solid, and time and place, besides." In order to shew that number is definite or discontinuous, he observes, "there is no common boundary whereon the parts of any number conjoin; as if, for instance, five or three be parts of ten, there is no common boundary whereon five or seven can conjoin to make the whole number, but each part is, for ever, a distinct number, and thus number is among definite quantities." "Words are, in like manner, among definite quantities; and it is manifest that words, uttered by the voice, are quantity, in that they are measurable by long and short syllables, and manifest too that there is no common boundary ​whereon the parts of a word, that is syllables, conjoin to make the whole sound, and thus that each is for ever a distinct sound. But a line, on the contrary, is continuous, as there is no common boundary whereon its parts, that is points, conjoin, as lines, to make a superficies, whereon all parts of the solid conjoin; so too time is continuous, for that which is present is conjoined with that which is past, as it is with that which is future." Aristotle^[13], having shewn that there are these opposite conditions of quantity, in a positive as in an abstract sense, defines an unit (ἡ μόνας) as being, in direct opposition to a point, without position or place; a line as being divisible only in one way; a superficies as divisible in two, and a solid, quantitatively considered, as divisible in three, and, indeed, in all ways. Number is still regarded, of course, as a collection of units; the superficies as that which has only length and breadth; and the solid as that which has length, breadth, and depth.

Note 6, p. 12. Among entities in potentiality or whether, &c.] These terms run, like a golden thread, through all the physiological works of Aristotle, and were adopted by him in order to distinguish virtual from actual condition or existence, the capability, that is, of becoming, by innate force or power, an entelechy or reality, which is the purport of the last term. They may be briefly exemplified thus: — an egg, e.g. is alive in potentiality — it has within it, that is, a principle, whereby, under genial ​circumstances, it can develope into a living being; and so a seed, while alive, is capable of becoming a perfect living plant, as the egg or the caterpillar or the chrysalis is, in potentiality, the future perfect insect or butterfly. The terms comprehend, in fact, all the metamorphic conditions of the animal and vegetable kingdoms, and have a range of application wide enough to include life under all degrees and forms. This was the first great idea in their adoption, and although Aristotle made them to signify an analogous transition in moral or mental faculties, (as when he speaks of a boy as a general, in potentiality,) yet their real purport is to distinguish those two universal conditions of living and sentient beings. Cicero^[14] has alluded to these terms or rather to the entelechy, (as was noted in the preface,) but, from not having contrasted it with the potentiality, he seems to have mistaken its general import; and he may thus have been led to suppose that Aristotle's intention, in this novel term, was to designate a special fifth nature, to be the source of motion and the originating cause of mental faculties and natural emotions. Montaigne^[15], also, in modern times, following Cicero, speaks of the entelechy only, which he regards, erroneously, as the motor power of the body — "ce qui naturellement fait mouvoir le corps." A hot dispute prevailed among scholars, it may be added, before and during the age of Rabelais^[16],(and which he has alluded to ​with all his wonted wit and learning,) whether the term should be ἐντελέχεια or ἐνδελέχεια; he was, evidently himself, one of the entelechists, as he says that the Lady Quint-essence, who had had Aristotle, "that paragon of all philosophy," for god-father, had been truly and correctly named Entelechy by him.

Note 7, p. 13. Whether the difference is generic or specific.] "The term Genus^[17] implies a continuous series of individuals having a like species or form, so that genus may be predicated of man, so long as there may be a continuous generation of human beings; the term again may be applied to the source whence individuals may have descended, and thus some Greeks are of the Hellenic, others of the Ionic genus, on account of their direct descent from Hellenus or from Ion. And this applies so much more to the progenitor than to external conditions, that the descendants from a female constitute a genus. Species^[18] implies the mode of being of the individual, together with the primal essence; and as the matter constitutive of the genus is in the species, so species may be regarded as parts of the genus. In modern classification, genus signifies "a distinct but subordinate group, which gives its name as a prefix to that of all the species of which it is composed." The physical sciences have been so widely developed, however, that, as those terms no longer suffice for grouping the myriads of beings which have been observed since Aristotle's time, naturalists ​have, in addition, adopted kingdom or class, order, sub-genus, individual, and variety.

Note 8, p. 13. The term animal, however, in an universal sense, &c.] This passage, which, in the original, is even more elliptical than its version, has engaged much of the attention of commentators without having been satisfactorily elucidated — some have explained it as a criticism of the ideas or archetypes of Plato; and others as an objection to every universal term, which, although an abstraction, is to typify actual beings; and this is, probably, the purport of the criticism. Thus^[19], "the origin of the controversy, during the middle ages, between the nominalists and realists, may be traced down to Aristotle and his followers." Wording so elliptical must, of course, be subject, according to the bias of opinions, to different interpretations; but if it imply objection to every abstract term which is to embody, so to say, realities, this version may be accepted as its interpretation. The Latin version^[20], however, is, "Animal autem universale aut nihil est aut posterius est, et quicquid itidem aliud communiter prædicatur;" and the French^[21], "C'est que l'animal pris en un sens universel ou n'est rien, ou bien n'est que quelque chose de très ultérieur."

Note 9, p. 13. The mind before thought, &c.] Aristotle^[22] says that among the philosophers who were engaged ​upon first causes, Anaxagoras and his predecessor Hermoticus had maintained that, as in animals there is a motor principle, so in nature there is mind, and that it is the cause as well of the universe as of universal order; and thus "they assumed at once that mind is the cause of the beautiful, the origin of being, and the source whence motion is derived for every thing living." Anaxagoras, in fact, regarded mind as the first cause of things (which Empedocles was rather disposed to assign to the principle of attraction, which he designated φιλία, and held to be an universal element), and maintained that, while all else is but a combination of particles, it is homogeneous, impassive, isolated, and pure. We are incapable, Aristotle observes, in his comment upon these opinions, of continuous thought and reflexion, because these are recreations too lofty to be continuously maintained; but, on this account, watching (not being asleep, that is), feeling and thinking are our most genial conditions, because from and through them, we derive our hopes and recollections. Notwithstanding, however, this acknowledgement, so to say, of mind, as a sovereign principle, and its attributes, there is no attempt to define its nature and its relations, or to shew in what it was identified with or different from the vital principle; and this want of critical distinction between them is the more apparent as several epithets (προγϵνϵστατός – θϵωρητικός – πρακτικός – παθητικός) are introduced in the course of these physiological treatises, which cannot but have modified the parent term. ​

Note 10, p. 15. Whether all the emotions of Vital Principle, &c.] These passages shew clearly the suggestive power and perspicacity of Aristotle's intellect, and they point so clearly to doctrines which had yet to be developed, that they cannot be studied without feelings of surprise as well as admiration. The brain^[23] was, in that age, supposed to be merely a supplementary organ to respiration; and, from its not giving out sensation when touched, and from imperfect anatomy, it was supposed to have no relation whatever with the sentient organs or spinal cord. The nerves, as cords of sensation, were unknown; the very term (νϵῦρον), which has been transferred to them as nerve, meant then tendon or sinew. Hence it is that, in modern languages, a man is said to be nervous in the one sense, and a delicate female to be nervous in the other. It was thus, from intuition and study, that Aristotle drew this train of suggestive reasoning upon the influences exercised over our passions and emotions by the organs of the body; that he discerned, that is, the seat and source of the temperaments. Bichat^[24], having a far wider range of anatomical knowledge was able, by assigning to the brain and ganglionic system their proper offices, to distinguish intellectual faculties from passions and emotions, which although human, still are temperamental and functional — to distinguish, that is, the animal from the organic life.

Note 11, p. 15. In the same way all the emotions, &c.] These passages are quite in accordance with all that ​physiology now teaches; for although but repetition, it may be said that Aristotle places the passions and emotions in the organic life, and shews "that every individual must be influenced by his particular temperament." Thus, as organs predominate, or may be more or less active, individuals are affected and modified, so to say, in temper as in character. The temperaments ought to be subordinated, of course, to the higher faculties; but those organs are abiding powers, and they are ever exercising an influence which it is for reason to control or subdue. Plato, in the Timæus, has discerned this great truth—a mortal principle (ὅτε τὸ θνητὸν ἐπεστέλλε γένος) is there assigned to the body, as the seat of the passions and coarser appetites, while the brain is represented as a soil fit for the divine seed of wisdom; and this will suffice to shew that this most gifted man, although but imperfectly acquainted with physiology, had perceived the co-existence in the human being of an intellectual and, so to say, a functional existence. Descartes^[25] seems to have adopted opinions concerning the "passions of the soul," which have much in common with those of Aristotle; but although so well acquainted with his writings, he does not appear to have studied this treatise.

Note 12, p. 16. But the physiologist and the metaphysician would, &c.] The difference here dwelt upon in the mode of accounting for the same phenomena, according to the bias given by studies or pursuits, will, it may ​be assumed, be of constant recurrence; for, as physical science advances, it will become more and more difficult for the same party to attain to a large and solid acquaintance with the attributes of mind (abstractions, that is), and the knowledge of "external nature." The self-same differences, in fact, which were delineated so graphically by Aristotle, are still to be traced in our almost exclusive attention to the physical sciences, and our disinclination to admit, in our inquiries, of any proof but such as can be tested through and by the senses and observation. The terms here rendered physiologist and metaphysician (terms unknown, by the way, to Aristotle) in the Latin version are naturalis, and disserendi artifex; that of artisan is faber; builder, artifex; and transcendental philosopher is primus philosophus.