§ 1. as a preparation for the inquiry which is the proper object of logic, namely, in what manner propositions are to be proved, we have found it necessary to inquire what they contain which requires, or is susceptible of, proof; or (which is the same thing) what they assert. in the course of this preliminary investigation into the import of propositions, we examined the opinion of the conceptualists, that a proposition is the expression of a relation between two ideas; and the doctrine of the nominalists, that it is the expression of an agreement or disagreement between the meanings of two names. we decided that, as general theories, both of these are erroneous; and that, though propositions may be made both respecting names and respecting ideas, neither the one nor the other are the subject-matter of propositions considered generally. we then examined the different kinds of propositions, and found that, with the exception of those which are merely verbal, they assert five different kinds of matters of fact, namely, existence, order in place, order in time, causation, and resemblance; that in every proposition one of these five is either affirmed, or denied, of some fact or phenomenon, or of some object the unknown source of a fact or phenomenon.

in distinguishing, however, the different kinds of matters of fact asserted in propositions, we reserved one class of propositions, which do not relate to any matter of fact, in the proper sense of the term, at all, but to the meaning of names. since names and their signification are entirely arbitrary, such propositions are not, strictly speaking, susceptible of truth or falsity, but only of conformity or disconformity to usage or convention; and all the proof they are capable of, is proof of usage; proof that the words have been employed by others in [pg 120]the acceptation in which the speaker or writer desires to use them. these propositions occupy, however, a conspicuous place in philosophy; and their nature and characteristics are of as much importance in logic, as those of any of the other classes of propositions previously adverted to.

if all propositions respecting the signification of words were as simple and unimportant as those which served us for examples when examining hobbes' theory of predication, viz. those of which the subject and predicate are proper names, and which assert only that those names have, or that they have not, been conventionally assigned to the same individual, there would be little to attract to such propositions the attention of philosophers. but the class of merely verbal propositions embraces not only much more than these, but much more than any propositions which at first sight present themselves as verbal; comprehending a kind of assertions which have been regarded not only as relating to things, but as having actually a more intimate relation with them than any other propositions whatever. the student in philosophy will perceive that i allude to the distinction on which so much stress was laid by the schoolmen, and which has been retained either under the same or under other names by most metaphysicians to the present day, viz. between what were called essential, and what were called accidental, propositions, and between essential and accidental properties or attributes.

§ 2. almost all metaphysicians prior to locke, as well as many since his time, have made a great mystery of essential predication, and of predicates which are said to be of the essence of the subject. the essence of a thing, they said, was that without which the thing could neither be, nor be conceived to be. thus, rationality was of the essence of man, because without rationality, man could not be conceived to exist. the different attributes which made up the essence of the thing were called its essential properties; and a proposition in which any of these were predicated of it was called an essential proposition, and was considered to go deeper into the nature of the thing, and to convey more important information [pg 121]respecting it, than any other proposition could do. all properties, not of the essence of the thing, were called its accidents; were supposed to have nothing at all, or nothing comparatively, to do with its inmost nature; and the propositions in which any of these were predicated of it were called accidental propositions. a connexion may be traced between this distinction, which originated with the schoolmen, and the well-known dogmas of substanti? secund? or general substances, and substantial forms, doctrines which under varieties of language pervaded alike the aristotelian and the platonic schools, and of which more of the spirit has come down to modern times than might be conjectured from the disuse of the phraseology. the false views of the nature of classification and generalization which prevailed among the schoolmen, and of which these dogmas were the technical expression, afford the only explanation which can be given of their having misunderstood the real nature of those essences which held so conspicuous a place in their philosophy. they said, truly, that man cannot be conceived without rationality. but though man cannot, a being may be conceived exactly like a man in all points except that one quality, and those others which are the conditions or consequences of it. all therefore which is really true in the assertion that man cannot be conceived without rationality, is only, that if he had not rationality, he would not be reputed a man. there is no impossibility in conceiving the thing, nor, for aught we know, in its existing: the impossibility is in the conventions of language, which will not allow the thing, even if it exist, to be called by the name which is reserved for rational beings. rationality, in short, is involved in the meaning of the word man: is one of the attributes connoted by the name. the essence of man, simply means the whole of the attributes connoted by the word; and any one of those attributes taken singly, is an essential property of man.

but these reflections, so easy to us, would have been difficult to persons who thought, as most of the later aristotelians did, that objects were made what they were called, that gold (for instance) was made gold, not by the possession of certain properties to which mankind have chosen to attach that name, but [pg 122]by participation in the nature of a certain general substance, called gold in general, which substance, together with all the properties that belonged to it, inhered in every individual piece of gold.[23] as they did not consider these universal substances to be attached to all general names, but only to some, they thought that an object borrowed only a part of its properties from an universal substance, and that the rest belonged to it individually: the former they called its essence, and the latter its accidents. the scholastic doctrine of essences long survived the theory on which it rested, that of the existence of real entities corresponding to general terms; and it was reserved for locke at the end of the seventeenth century, to convince philosophers that the supposed essences of classes were merely the signification of their names; nor, among the signal services which his writings rendered to philosophy, was there one more needful or more valuable.

now, as the most familiar of the general names by which an object is designated usually connotes not one only, but several attributes of the object, each of which attributes separately forms also the bond of union of some class, and the meaning of some general name; we may predicate of a name which connotes a variety of attributes, another name which connotes only one of these attributes, or some smaller number of them than all. in such cases, the universal affirmative proposition will be true; since whatever possesses the whole of any set of attributes, must possess any part of that same set. a proposition of this sort, however, conveys no information to any one who previously understood the whole meaning of the terms. the propositions, every man is a corporeal being, every man is a living creature, every man is rational, convey no knowledge to any one who was already aware of the entire meaning of the word man, for the meaning of the word [pg 123]includes all this: and that every man has the attributes connoted by all these predicates, is already asserted when he is called a man. now, of this nature are all the propositions which have been called essential. they are, in fact, identical propositions.

it is true that a proposition which predicates any attribute, even though it be one implied in the name, is in most cases understood to involve a tacit assertion that there exists a thing corresponding to the name, and possessing the attributes connoted by it; and this implied assertion may convey information, even to those who understood the meaning of the name. but all information of this sort, conveyed by all the essential propositions of which man can be made the subject, is included in the assertion, men exist. and this assumption of real existence is, after all, the result of an imperfection of language. it arises from the ambiguity of the copula, which, in addition to its proper office of a mark to show that an assertion is made, is also, as formerly remarked, a concrete word connoting existence. the actual existence of the subject of the proposition is therefore only apparently, not really, implied in the predication, if an essential one: we may say, a ghost is a disembodied spirit, without believing in ghosts. but an accidental, or non-essential, affirmation, does imply the real existence of the subject, because in the case of a non-existent subject there is nothing for the proposition to assert. such a proposition as, the ghost of a murdered person haunts the couch of the murderer, can only have a meaning if understood as implying a belief in ghosts; for since the signification of the word ghost implies nothing of the kind, the speaker either means nothing, or means to assert a thing which he wishes to be believed to have really taken place.

it will be hereafter seen that when any important consequences seem to follow, as in mathematics, from an essential proposition, or, in other words, from a proposition involved in the meaning of a name, what they really flow from is the tacit assumption of the real existence of the objects so named. apart from this assumption of real existence, the class of propositions in which the predicate is of the essence of the subject [pg 124](that is, in which the predicate connotes the whole or part of what the subject connotes, but nothing besides) answer no purpose but that of unfolding the whole or some part of the meaning of the name, to those who did not previously know it. accordingly, the most useful, and in strictness the only useful kind of essential propositions, are definitions: which, to be complete, should unfold the whole of what is involved in the meaning of the word defined; that is, (when it is a connotative word,) the whole of what it connotes. in defining a name, however, it is not usual to specify its entire connotation, but so much only as is sufficient to mark out the objects usually denoted by it from all other known objects. and sometimes a merely accidental property, not involved in the meaning of the name, answers this purpose equally well. the various kinds of definition which these distinctions give rise to, and the purposes to which they are respectively subservient, will be minutely considered in the proper place.

§ 3. according to the above view of essential propositions, no proposition can be reckoned such which relates to an individual by name, that is, in which the subject is a proper name. individuals have no essences. when the schoolmen talked of the essence of an individual, they did not mean the properties implied in its name, for the names of individuals imply no properties. they regarded as of the essence of an individual, whatever was of the essence of the species in which they were accustomed to place that individual; i.e. of the class to which it was most familiarly referred, and to which, therefore, they conceived that it by nature belonged. thus, because the proposition man is a rational being, was an essential proposition, they affirmed the same thing of the proposition, julius c?sar is a rational being. this followed very naturally if genera and species were to be considered as entities, distinct from, but inhering in, the individuals composing them. if man was a substance inhering in each individual man, the essence of man (whatever that might mean) was naturally supposed to accompany it; to inhere in john thompson, and to form the common essence of thompson and julius c?sar. it might then be [pg 125]fairly said, that rationality, being of the essence of man, was of the essence also of thompson. but if man altogether be only the individual men and a name bestowed upon them in consequence of certain common properties, what becomes of john thompson's essence?

a fundamental error is seldom expelled from philosophy by a single victory. it retreats slowly, defends every inch of ground, and often, after it has been driven from the open country, retains a footing in some remote fastness. the essences of individuals were an unmeaning figment arising from a misapprehension of the essences of classes, yet even locke, when he extirpated the parent error, could not shake himself free from that which was its fruit. he distinguished two sorts of essences, real and nominal. his nominal essences were the essences of classes, explained nearly as we have now explained them. nor is anything wanting to render the third book of locke's essay a nearly unexceptionable treatise on the connotation of names, except to free its language from the assumption of what are called abstract ideas, which unfortunately is involved in the phraseology, though not necessarily connected with the thoughts contained in that immortal third book.[24] but, besides nominal essences, he admitted real essences, or essences of individual objects, which he supposed to be the causes of the sensible properties of those objects. we know not (said he) what these are; (and this acknowledgment rendered the fiction comparatively innocuous;) but if we did, we could, from them alone, demonstrate the sensible properties of the object, as the properties of the triangle are [pg 126]demonstrated from the definition of the triangle. i shall have occasion to revert to this theory in treating of demonstration, and of the conditions under which one property of a thing admits of being demonstrated from another property. it is enough here to remark that, according to this definition, the real essence of an object has, in the progress of physics, come to be conceived as nearly equivalent, in the case of bodies, to their corpuscular structure: what it is now supposed to mean in the case of any other entities, i would not take upon myself to define.

§ 4. an essential proposition, then, is one which is purely verbal; which asserts of a thing under a particular name, only what is asserted of it in the fact of calling it by that name; and which therefore either gives no information, or gives it respecting the name, not the thing. non-essential, or accidental propositions, on the contrary, may be called real propositions, in opposition to verbal. they predicate of a thing some fact not involved in the signification of the name by which the proposition speaks of it; some attribute not connoted by that name. such are all propositions concerning things individually designated, and all general or particular propositions in which the predicate connotes any attribute not connoted by the subject. all these, if true, add to our knowledge: they convey information, not already involved in the names employed. when i am told that all, or even that some objects, which have certain qualities, or which stand in certain relations, have also certain other qualities, or stand in certain other relations, i learn from this proposition a new fact; a fact not included in my knowledge of the meaning of the words, nor even of the existence of things answering to the signification of those words. it is this class of propositions only which are in themselves instructive, or from which any instructive propositions can be inferred.[25]

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nothing has probably contributed more to the opinion so long prevalent of the futility of the school logic, than the circumstance that almost all the examples used in the common school books to illustrate the doctrine of predication and that of the syllogism, consist of essential propositions. they were usually taken either from the branches or from the main trunk of the predicamental tree, which included nothing but what was of the essence of the species: omne corpus est substantia, omne animal est corpus, omnis homo est corpus, omnis homo est animal, omnis homo est rationalis, and so forth. it is far from wonderful that the syllogistic art should have been thought to be of no use in assisting correct reasoning, when almost the only propositions which, in the hands of its professed teachers, it was employed to prove, were such as every one assented to without proof the moment he comprehended the meaning of the words; and stood exactly on a level, in point of evidence, with the premises from which they were drawn. i have, therefore, throughout this work, avoided the employment of essential propositions as examples, except where the nature of the principle to be illustrated specifically required them.

§ 5. with respect to propositions which do convey information—which assert something of a thing, under a name that does not already presuppose what is about to be asserted; there are two different aspects in which these, or rather such of them as are general propositions, may be considered: we may either look at them as portions of speculative truth, or as memoranda for practical use. according as we consider propositions in one or the other of these lights, their import may be conveniently expressed in one or in the other of two formulas.

according to the formula which we have hitherto employed, and which is best adapted to express the import of the proposition as a portion of our theoretical knowledge, all men are mortal, means that the attributes of man are always accompanied by the attribute mortality: no men are gods, means that the attributes of man are never accompanied by [pg 128]the attributes, or at least never by all the attributes, signified by the word god. but when the proposition is considered as a memorandum for practical use, we shall find a different mode of expressing the same meaning better adapted to indicate the office which the proposition performs. the practical use of a proposition is, to apprise or remind us what we have to expect, in any individual case which comes within the assertion contained in the proposition. in reference to this purpose, the proposition, all men are mortal, means that the attributes of man are evidence of, are a mark of, mortality; an indication by which the presence of that attribute is made manifest. no men are gods, means that the attributes of man are a mark or evidence that some or all of the attributes understood to belong to a god are not there; that where the former are, we need not expect to find the latter.

these two forms of expression are at bottom equivalent; but the one points the attention more directly to what a proposition means, the latter to the manner in which it is to be used.

now it is to be observed that reasoning (the subject to which we are next to proceed) is a process into which propositions enter not as ultimate results, but as means to the establishment of other propositions. we may expect, therefore, that the mode of exhibiting the import of a general proposition which shows it in its application to practical use, will best express the function which propositions perform in reasoning. and accordingly, in the theory of reasoning, the mode of viewing the subject which considers a proposition as asserting that one fact or phenomenon is a mark or evidence of another fact or phenomenon, will be found almost indispensable. for the purposes of that theory, the best mode of defining the import of a proposition is not the mode which shows most clearly what it is in itself, but that which most distinctly suggests the manner in which it may be made available for advancing from it to other propositions.