A manual of logic, deductive and inductive

Preface

The object contemplated in the following pages is to present the tyro with a succinct, yet comprehensive, view of Logic in the simplest possible form.

Instruction in Logic is now no longer confined to Colleges and Universities : it has been introduced into many of our schools and academies ; and it is hoped that an effort to simplify, without compromising, the distinctive characteristics of a study, so elegant in its nature, and so highly calculated to train the youthful mind to correct habits of thought, may not be unacceptable to the latter class of seminaries.

The writer has been induced to this undertaking, from its having appeared to him, when employed as a tutor in Logic, that an elementary manual, more simple in its phraseology, and more copious in illustrations and examples, than any of the treatises now in use, might tend, in some measure, to facilitate an earlier and easier acquaintance with the science than is at present attainable.

In the hope of securing this object, the use of abstract symbols in illustration has been almost entirely dis-

a2

11 PREFACE.

carded; for although convenient for the compiler of a logical treatise, and intelligible to the advanced student, they are invariably uninteresting, if not repulsive, to the beginner.

Simplicity has been invariably adhered to, in selecting examples, alike in propositions and syllogisms ; but it is hoped that they are not of such a nature as to incur the charge of triviality, so frequently brought against works on Logic, owing to the meagreness of the illustrations usually employed.

The conflicting views entertained, regarding the true province of Logic, surround the publication of an elementary treatise with peculiar difficulties. Any person, however, who has duly considered the matter, can have little difficulty in deciding, that if Logic is to be considered a distinct and self-sufficient scientific art, the formal view must be adopted ; for this is the only aspect under which its proper function can be adequately defined and defended. It is possible, however, that the disciples of the formal school, in their abhorrence of the material and verbal views, have somewhat overstrained their own theory ; and that, in order to arrive at a yet more satisfactory definition, they must either agree to a slight compromise, or reject, as extralogical, many matters admitted at present into logical works. #

In declaring his adhesion to the formal view of the province of Logic, the writer readily admits that he has introduced into the following pages much that is extra-

PREFACE. Ill logical; and his apology is, that his object was not to vindicate any particular theory, but rather to lay before the tyro whatever seemed most useful as an introduction to the subject, more particularly as it has not as yet been determined to what special branch of knowledge matters now deemed extralogical are to be assigned.

The discussion of vexed questions has been altogether excluded from the text, as their introduction seemed inconsistent with the plainness requisite in an elementary work; but when considered necessary, they have been adverted to in Notes.

To the authors of the many very valuable works on Logic, which have recently emanated from Oxford, the writer gratefully acknowledges his obligations. The treatises alluded to are obviously intended to supply the defects and correct the errors of the University Textbook, with such additions as have seemed necessary to prepare students for the present high standard of logical examinations. But although extremely valuable in this respect, the works referred to have left the necessity of a work purely introductory unsupplied.

The writer also willingly acknowledges the benefits he has derived from the unrivalled article by Sir W. Hamilton in the ' Edinburgh Eeview/ as may be seen from the ample use made of its contents throughout this Manual. To this article the more correct views of the province of Logic, recently adopted in this country, are mainly attributable.

IV PREFACE.

It was originally intended to treat of Inductive Logic at some length in this Manual; but the unexpected space -which Deductive Logic has occupied, has rendered a full consideration of it incompatible with the publishing arrangements of the present edition.

Glasgow, January, 1850.

Contents

Page

Introduction, ....... ix

Chapter I

Section I. Heads of the Ancient Logic — Simple Apprehension, Judgment, Reasoning — General Explanation of this Division — Rationale of this Division — Notes, .... 1-4

Section II. Definition of Simple Apprehension — Divided into Incomplex and Complex — Incomplex Apprehension explained — Complex Apprehension explained — Simple Terms explained — Simple Terms may consist of one or more Words — Errors incident to Simple Apprehension, Judgment, and Reasoning — Terms defined— Divided into Simple, Complex, and Decomplex — Simple Terms — Categorematic, Syncategorematic, and Mixed — Simple Terms explained according to this Division — Complex Terms explained — Decomplex Terms explained — Definition of the Logical Term — The Logical Term divided into Singular and Common — Singular and Common Terms explained — Various Names applicable to Common Terms — Notes, . . . 4-24

Section I. Abstraction explained and illustrated — Generalisation

explained and illustrated — Nominalism and Realism — Notes, 24-32

CONTENTS.

Page

Section II. Extension and Comprehension of Terms explained- Scheme of Extension and Comprehension, . . . 32-37

Section III. The Predicables — General Explanation, with Examples— Scheme of the Porphyrian Tree — Definition and Explanation of Genus — Definition and Explanation of Species — Scheme of Subaltern Genera and Infimse Species — Definition and Explanation of Differentia — Divided into Generic and Specific — Definition and Explanation of Proprium — Divided into Generic and Specific — Definition and Explanation of Accidens — Scheme of the Heads of Predicables, with their Subdivisions, . . . 37-62

Section IV. The Categories or Predicaments — Enumeration of them — Aristotelic Enumeration adopted, as simplified by Sir W. Hamilton — Classifications of Locke, Hume, Kant, Mill, Thomson, 64-69

Section V. Division — Rules of Logical Division — Logical Wholes

of Extension and Comprehension — Boethius on Division — Notes, 69-75

Section VI. Definition — Definition of two kinds — Nominal and

Real — Rules of Definition — Aristotle's view of Definition, . 75-83

Section VII. Of the Distribution of Terms— Of the Subject— Of the Predicate, ...... 83-88

Chapter III

Section I. Judgment — Simple Propositions — Division of Propositions— Substance of Propositions — Quality of Propositions — Quantity of Propositions — Notes, .... 89-104

Section II. Modality of Propositions — Examination of Aristotle's four Modes, . . . . . . . 104-110

Section III. The Opposition of Propositions— Subaltemation

CONTENTS. Vll

Page Contrary Opposition — Sub-contrary Opposition — Contradictory

Opposition — Opposition of Singular Propositions, . . 110-121

Section IV. Conversion of Propositions — Simple Conversion — Conversion of Universal Negatives — Conversion of Particular Affirmatives — Conversion per Accidens — Conversion of Universal Affirmatives — Conversion of Universal Negatives — Conversion by Contraposition or Negation, ..... 122-130

Chapter IV

Section I. Of Syllogism — Rules of Syllogism — Canons — Rules of Syllogism of two kinds — General and Special — General Rules explained and exemplified — Special Rules explained and exemplified— Figures of Syllogism — Moods of Syllogism, . ^ 130-163

Section II. Reduction of Syllogisms — Reduction, of two kinds — Direct and Indirect — Examples, .... 163-176

Section III. Reductio per Impossible or ad Absurdum — Examples— Compound Propositions, .... 176-186

Section V. Of the Dilemma — Destructive and Constructive. Examples, ....... 192-201

Section VI. Of the Enthymeme — Aristotelic view of the Enthymeme — Ordinary view — Rules — Examples, . . . 201-208

Section VII. Of the Epicheirema — Explanation — Examples, 208-210

Section VIII. Of the Sorites — Its meaning as a species of argumentation-—Expanded into separate Syllogisms — Rules — Examples— The Goclenian Sorites explained, . . . 211-218

Vlll CONTENTS.

Page Section IX. Of the Example — Different from Induction — Examples, ....... 218-220

Section X. Of Sophisms — Divided into Fallacies in the Expres-- sion, and Fallacies in the Matter — Both kinds explained and exemplified — Of Induction — Explained as understood by Aristotle— Views of the nature of Induction examined — Aristotelian view adopted, 220-236

INTKODUCTION

The conflicting opinions entertained by writers on Logic, as to its proper province, and also as to whether it is an art or science, or both, verifies the adage — Omnis dejinitio periculosa est, Aristotle has unfortunately left us no definition of Logic ; and from the mixed nature of the contents of the Organon, it would certainly have been difficult to do so.

That Logic is both a science and an art has always been admitted by every one acquainted with its proper province and nature. It is a science, inasmuch as by analysing the elements, principles, and structure of arguments, it teaches us how to discover their truths, or detect their fallacies, and point out the sources of such errors. It is an art, inasmuch as it teaches us to arrange arguments in such a manner as that their truth may be most readily perceived, or their falsehood detected.

It would be out of place here to enter on an examination of many definitions, as it would be an unprofitable encroachment on space that may be more usefully occupied. It is only intended, therefore, to consider briefly those of Dr Eeid, Archbishop Whateley, and Sir William

Hamilton.

b

X INTRODUCTION.

According to Eeid, the professed end of Logic is ' to teach men to think, judge, and reason, with precision and accuracy! This definition is evidently founded on the usual division of the cognitive faculties, and, on this account, must be considered at least ingenious. 'To think' is obviously intended to refer to simple apprehension — 'judge/ to judgment, mental or verbal — and 'reason,' to syllogism. But this distribution of the cognitive faculties is itself a cross- division, for the dividing members are not distinct. They run into one another, and consequently the same fault characterises the definition founded on them. Logic is certainly furnished with its own peculiar rules and canons ; but rules, in any science, can never be employed for the discovery or investigation of truth. Their sole use and end is to guard against error. If this definition were to be admitted, all known sciences might be at once stripped of their distinctive appellations, and be indiscriminately classed under the name — Logic. The grand error in this definition is, however, that it confounds the material with the logical; in other words, the process of investigation with the inference necessitated by the laws of thought. Logic has nothing to do with things as they exist really and in themselves, but only the forms of thought under which the mind conceives them. It is conversant solely about second, not Jirst notions. Hence, a logical inference is not determined by any objective casualty subsisting between the terms of the premisses and conclusion, but solely the subjective relation of reason and consequence under which they are construed to the mind in thought. The question whether the premisses of an argument in any objective science are true, is, no doubt, a very important one ; but the logician, as such, cannot be called upon to answer it. He may be able to

INTRODUCTION. XI

answer it, but it will be as an Astronomer, Chemist, Geologist, Botanist, &c, as the case may be, but not as a logician ; for as a logician he is merely responsible for the soundness of the consequent on the assumed truth of the antecedent. The merit of the correct antecedent is material of the correct consequent logical. Cuique in sua arte credendum.

In Archbishop Whateley's opinion, 'Logic is the art of employing language properly for the purpose of reasoning.' This definition restricts the province of Logic to the regulation of language. It may be a slight improvement on the definition of Hobbes, viz., that Logic is 'the art of computation ' — a kind of mental arithmetic, not conducted by figures, but by words. We add, for instance, two terms to make an affirmation, two affirmations to make a syllogism, and many syllogisms to make a demonstration. There is undoubtedly an intimate connection between thought and language; but the regulation of language falls within the province of grammar, not of Logic ; for if it were, thought would necessarily be considered a function of a language, instead of language being a function of thought. On this definition, the pointed remarks of Mr Chretien are conclusive : ' If thought be only a function of language, man is better characterised as a speaking than as a reasoning being; for it is more natural and more scientific to define by the cause than the effect. And then, to draw any such inference from man's possessing reason, as that his actions are therefore probably free, or his thinking nature immortal, becomes at once absurd ; for none will assert such liberty or immortality to be a consequence of speech, of which reason itself is on this theory a consequence.' a

a Essay on Logical Method, by Charles P. Chretien, M.A., Oxford.

Xll INTRODUCTION.

Sir William Hamilton defines Logic to be ' the science of the laws of thought as thought — that is, of the necessary conditions to which thought, considered in itself, is subject. This is technically called its form' This definition is probably intended as an improvement on that given by Kant, viz., c the science of the necessary laws of the understanding and the reason.' The definition of Kant may be simplified by the explanation, that the inferences of opposition and conversion are considered by him as syllogisms of the understanding, and the usual form of syllogisms as the syllogisms of the reason. Sir William Hamilton's definition is here adopted.

In connection with this definition, the foregoing brief introductory remarks may be very appropriately closed with the following judicious passage from Mr Mansel: — 'It is not intended to deny the usefulness of Logic ; but it may safely be asserted, that its more valuable fruits are to be found in the training which the mind unconsciously receives, than in the conscious employment of knowledge in the formation and examination of reasonings, and that both, in respect of the true character of the science, are secondary and accidental results — not primary and essential features.'

MANUAL OF LOGIC.

CHAPTER L SECTION I.

The ancient Logic consisted of three heads, viz., Simple Apprehension,* Judgment, and Reasoning. The earlier Logicians considered these, in so far as the province of Logic was concerned, as the only operations of the mind. From its convenience, this distribution of the cognitive faculties has still been followed.

Under the first head, viz., Simple Apprehension, notions are treated of, and these notions, when expressed in words, are called simple terms.

The second head, viz., Judgment, treated of the agreement or disagreement of any two notions, whether incomplex or complex, when compared together in the mind; and this comparison is termed a judgment, (a-ro^ai/cvc) and when verbally expressed, a ■proposition (Kgoraac).

The third head, viz., Reasoning, treated of syllogism, or the manner in which, from two judgments or propositions related

a There is no phrase in Aristotle exactly corresponding to simple apprehension : the nearest is r\ ruv adiaigerwv vorjffig — the apprehension of uncompounded notions; vorjtfig is, however, not restricted to any specific meaning by Aristotle.

A to each other, the mind proceeds to a third judgment or proposition, founded upon and resulting from them.

This division11 of the mental powers, although objectionable, is at all events recommended by its simplicity. Its rationale is as follows : —

1. We first acquire simple notions ; from these we proceed to notions of a more complex character, and to the mental faculty by which these two classes of notions are acquired we give the name, Simple Apprehension.

2. In virtue of our mental constitution, when once possessed of notions, we begin to compare them ; in other words, we institute mental judgments1* as to whether the notions or ideas we have acquired by simple apprehension, agree or disagree with each other ; and the judgments thus formed, when expressed in words, we term propositions.

A proposition consists of a subject, predicate and copula. The subject is that of which something is affirmed or denied ; the predicate that which is affirmed or denied of the subject ; and the copula that which unites the subject and predicate; as

Knowledge is power ; — or disjoins the subject and predicate ; as,

Predacious animals are — not ruminant.

a On this division Sir W. Hamilton remarks : — ' The division in question, I make bold to say, never was proposed by any philosopher, as a psychological distribution of the cognitive faculties in general ; on the contrary, it is only a hgical distribution of that section of the cognitive faculties which we denominate discursive, as those alone which are proximately concerned in the process of reasoning or thought, in its strictest signification.' — ReioVs Works, p. 242.

b Reid defines judgment to be an act of the mind whereby one thing is affirmed or denied of another. On this definition Mansell remarks very properly, ( Rudimenta, p. 3) : ' Thing is vague enough ; but it is not easy to comprehend the various kinds of judgment under any more precise expression. The terms of a judgment are not always objects of perception, and the very notions of agreement and disagreement are the consequences of judgment, not the conditions of possibility. In fact, judgment is as necessary to apprehension as apprehension to judgment.'

The substantive verb, in the present tense, is the affirmative copula. With the negative particle not affixed, it constitutes the negative copula. The affirmative judgment is sometimes called composition (twdsas), because it unites the two conceptions compared. The negative is sometimes called division (diuigstfig), because, on the other hand, it separates the two conceptions compared.

When comparing ideas, we find agreements to be either total or partial, and also disagreements to be either total or partial. Hence an affirmative proposition4 may be either universal* or particular f and a negative proposition5 also universal or particular.

3. In a syllogism we alternately compare two terms (the major and minor) with a third, called the middle term ; and in this way we ascertain whether the two terms, alternately compared with it, agree or disagree with each other.

A regular syllogism consists of three propositions : the two first are called the premisses, and the last the conclusion. In the premisses, the two terms whose agreement or disagreement is sought to be proved, are compared with the middle term, and the new proposition resulting from them is called the conclusion, e. g. —

Every effect is the result of an adequate cause.

The world is an effect ; therefore,

The world is the result of an adequate cause.

No ruminant animals are predacious.

The lion is predacious ; therefore, The lion is not a ruminant animal.

This division of the cognitive faculties into three distinct parts does not imply that they are altogether independent of each other. A progressive connection exists between them ;

c Kara, fisoog. d avrotpaffig — oratio negaus.

* MANUAL OF LOGIC.

and in the view of the logician, apprehension must be considered in its reference to judgment, and judgment in its relation to discourse/

All sciences have their technicalities, and without them no science would be intelligible. Apprehension, judgment, and reasoning, are the names by which logicians have agreed to express the faculties of obtaining evidence, whether intuitive or deductive ; and they stand to each other in the relation of simple, complex, decomplex. h

It will be seen from the foregoing

1. That a notion obtained by simple apprehension, when expressed in words, is called a term.

2. That an act of judgment is expressed by a proposition; and,

3. That an act of reasoning, when stated in regular form, is termed a syllogism.

These three heads will be more fully illustrated in their proper places.

a The relation subsisting between the three acts of thought is expressed in both these nomenclatures ; the one (simple, complex, decomplex) implying the synthetical advance from apprehension to judgment and discourse ; the other (syllogism, proposition, term) resolving, analytically, the complete and final act into its component judgments and apprehensions. — Woolley, p. 19.

b In speaking of this division, Reid states (Inquiry, cap. 7) : — 'The second includes the first, and the third includes both the first and second, but the first may be exercised without either of the other two.' On this opinion Sir W. Hamilton remarks: 'Apprehension is as impossible without judgment as judgment is impossible without apprehension. The apprehension of a thing or notion is only realised in the mental affirmation, that the concept ideally exists; and this affirmation is a judgment. In fact, all consciousness supposes a judgment, as all consciousness supposes a discrimination.'— ReioVs Works, p. 242. To the same effect is the following passage from Aquinas (in Perihenn, lect. 1) : ' Harum autem operationum prima ordinatur ad secundam ; quia non potest esse compositio et divisio nisi simplicium apprehensorum. Secunda vero ordinatur ad tertiam : quia videlicet oportet quod ex aliquo vero cognito, cui intellectus assentiat, procedatur ad certitudinem accipiendam de aliqaibus ignotis.'

MANUAL OF LOGIC.

SECTION II.

SIMPLE APPREHENSION^

Simple apprehension is defined to be the mere intellectual conception of a thing.b It is of two kinds, viz., incomplex and complex. Incomplex apprehension is prior in point of time.

INCOMPLEX APPREHENSION.

Incomplex apprehension properly implies simple uncompounded notions ; but, for the purposes of the logician, it is sufficient to consider all apprehensions incomplex which are verbally expressed by one word, whether that word repre^ sents a simple or compound notion.0

Simple notions or intuitions are obtained immediately by the mind, and they cannot be analysed into any elements

a It may be remarked, that the term simple apprehension is often indiscriminately used to denote either the faculty of simple apprehension, or an act of this supposed faculty; in other words, the mental power, or the notion acquired by it. It may be observed also, that the words perception and conception are also frequently used to denote either the act or the object. This ambiguity, against which the English language does not provide, is completely obviated by the Latin. A perception (perceptio) denotes the mere act of perceiving ; a. percept (perceptum) denotes the result of the act. In like manner, a conception (conceptio) signifies the mere act of conceiving, while a concept (conceptual) signifies the thing conceived.

Mr Mansell is of opinion, that simple apprehension is synonymous with conception, in the proper sense of the term. This is true with regard to mediate, but not immediate, notions.

b Nudus rei conceptus intellectivus. — Aldrich.

c Any one word (whether representative of a simple or a compound idea) denotes an incomplex simple apprehension in its logical sense. So also any number of words, when combined so as to form a sentence, become representative of complex apprehension. — Huyshe, p. 2.

Incomplex apprehension is of one object, or of several without any order or reference ; as, a king, a throne. Complex apprehension is of several objects, with such order or reference ; as, a king upon a throne. — Jackson, p. 2.

b MANUAL OF LOGIC.

more simple than themselves. Compound notions, on the other hand, are obtained mediately; that is, they are the results of many previous mental states.*1

It is by incomplex apprehension, that the mind acquires the notions represented by each word in a sentence, when the words are considered separately. The term ' incomplex ' cannot be affirmed of any notion denoted by a combination of words that have a grammatical relation to each other, with the exception of such combinations as, ' a street,' ' a palace,' &c.

COMPLEX APPREHENSION.

Any combination of words grammatically related, but not forming a proposition, represents a complex notion ; as, ' a member of Parliament/ ' the balance of power,' ' a regiment of soldiers.' In contradistinction to incomplex apprehension, complex apprehension represents the notions implied by all the words of a sentence taken collectively. The notions acquired, both by incomplex and complex apprehension, are expressed by simple terms.

SIMPLE TERMS.

A simple term is one or more words, expressing the subject of a proposition, or what is affirmed of that subject. The subject of a proposition may be expressed by one or more words ; as, time, wisdom, a troop of cavalry ; and so also may what is affirmed of any subject ; as, invaluable, from on high, advancing to battle. If we join these subjects by a copula, to what is affirmed of them respectively, we shall have two terms in each proposition, and no more, e. g. —

Time is invaluable.

Wisdom is from on high.

A troop of cavalry is advancing to battle.

a A perception immediate and individual, is an intuition ; the same mediate, and by means of a mark common to many things, is a conception. — 8. T. Coleridge.

A proposition, in which the copula and predicate are separated— as, magna est Veritas — is said to be tertii adjacentis; and a proposition, in which the copula and predicate form one word — as, aves volant, is said to be secundi adjacentis*

A simple term, whatever number of words it may contain, must not be confounded with a sentence or proposition containing Si judgment. In a simple term there is nothing affirmed or denied. It is a collection of words grammatically related, but not connected by a copula, and may be either the subject or predicate of a proposition, but not the whole of a proposition, e. g., Burton's Anatomy of Melancholy, is a simple term ; but Burton's Anatomy of Melancholy is remarkable for learning and research, is a proposition.

As the correctness of simple acts of judgment, as well as of prolonged processes of reasoning, depends on the clearness and distinctness of our apprehensions, this head of the ancient logic treats of the logical instruments that direct us in apprehending well, and the chief instruments are definition and division. Our notions themselves may be obscure, or their verbal expression may be indistinct. Hence the error incident to apprehension is indistinctness.

Indistinctness in our apprehensions may arise either from the imperfections of our faculties, or from a limited knowledge of the objects of which we form our conceptions. In the former case the indistinctness is unavoidable, e. g., Our conceptions of the Divine Being, his attributes, heaven and angels, and of whatever is only communicated to us by revelation, must be obscure. In the latter case the indistinctness is accidental, and may be remedied by study and observation. In all cases, the distinctness or indistinctness of our apprehensions will depend on our acquaintance with the object-matter. For without a definite and accurate knowledge of

a This distinction is recognised by Aristotle, but he does not deem it necessary that the latter should be resolved into the former. It was among the Latin commentators that the distinction first acquired prominence.

the meaning of terms, we cannot reason about them with an assurance that they are full and true representatives of the things signified.

The error incident to the faculty of judgment is falsity, and arises from asserting the agreement or disagreement of things according to the knowledge we possess regarding them, and not as they are in themselves. Hence such incorrect judgments; as,

The earth is stationary.

The surface of the earth is a plane.

Dews fall from the air.

Moonlight is cold.

The sun rises from the sea upwards.

The eye judges of distance and magnitude intuitively.

Judgment is liable to be misled by the senses, authority, example, and the passions.

The error incident to reasoning is & faulty mode of inferring (mendosa collectio.)a If our previous apprehensions are indistinct, and our judgments regarding them false, new judgments deduced from them cannot fail to be erroneous, e. g., Sonesty is the whole of religion ; therefore, I may indulge in excess with impunity. Qui sapit pauca loquitur ; pauco loquor ; ergo, sapio. It frequently happens, on the other hand, that from true premisses a false inference is deduced.b

The object of logic is to obviate these defects, by prescribing rules for our guidance alike in investigation and inference.

a Mendosa collectio is remedied by the rules of syllogism and induction ; and • here logic not only enables us to perform the operation rightly, but also to test the correctness of any given argumentation Mansell, p. 6.

b The Melitans drew an erroneous conclusion, when they reasoned thus : This stranger is about to be hilled by a venomous serpent ; therefore, he is a murderer pursued by vengeance. Nor was their subsequent inference less erroneous, when, in consequence of his shaking off the animal without injury, they said he teas a god.

MANUAL OF LOGIC.

TERMS.

A term has been defined to be a vicarious sign of a thing or idea used by conventional agreement*

A term is the sign of a thing when it represents an object known by any particular sound, or combination of sounds. It is the sign of an idea when it conveys by being uttered the same idea to the hearer's mind which the speaker had in his own. It is a vicarious sign, because it not only conveys the idea of an object, but it also supplies the place of that object. b

Whatever sounds, therefore, are not ex instituto, i. e., ratified by conventional agreement or mutual consent, cannot be considered terms — such as groans, shrieks, exclamations, &c, which are suggested by nature.

Terms are divided into three classes — simple, complex, and decomplex. c

a Signum rei vel conceptus ex instituto vicarium. — Aldrich. The term 'signum' is somewhat indefinite, for anything may b& made a sign, whether vocal or not, by conventional agreement. ' Signum vocale' would remove all ambiguity.

In M. Duval Jouve's Logic, p. 201, language is thus divided, — ( Absolute — Cries and Gestures. \ Conventional — Speech.