The laws of discursive thought, being a text-book of formal logic

Front matter

o cr x^ N , op 1 :

*

4 -7",

Preface

If we look back half a century we find Formal Logic taught in nearly all the colleges of Great Britain and America, but exercising an influence infinitely less than nothing (to use a phrase of Plato's) on the thought of the countries. Some of the professors and tutors were expounding it in a dry and technical manner, which wearied young men of spirit, and bred a distaste for the study ; while others adopted an apologetic tone for occupying even a brief space with so antiquated a department, and threw out hints of a new Logic as about to appear and supersede the old. The lingering life maintained by that old Aristotelian and Scholastic Logic, in spite of the ridicule poured upon it by nearly all the fresh thinkers of Europe for two or three centuries after the revival of letters, is an extraordinary fact in the history of philosophy ; I believe it can be accounted for only by supposing that the syllogism is substantially the correct analysis of the process which passes through the mind in reasoning. Certain it is that no proffered logical system has been able to set aside the Aristotelian, whether devised by Ramus, by the school of Descartes, the school of Locke, or the school of Condillac ; all have iv PREFACE.

disappeared after creating a brief expectation followed by a final disappointment. It is a remarkable circumstance that the revived taste for Togical studies in the last age proceeded from a restoration of the old Logic by two distinguished men, both reformers in their way, but both admirers of the Analytic of Aristotle. I refer to Archbishop Whately and Sir William Hamilton.

Whately first gave his views to the public in an article in the Encyclopcedia Metropolitana, which was expanded into his Elements of Logic in 1826. The publication constitutes an era in the history of the study in Great Britain and America. The admirable defence of the old Logic against the objections of such men as Principal Campbell and Dugald Stewart, and still more, the fresh and apt examples substituted for the dry stock ones which had been in use for a thousand or two thousand years, speedily attracted the favorable attention of the young thinkers of the times ; and Aristotle was once more in the ascendant. But while Whately's Elements is an interesting and healthy work, it can scarcely be described as specially a philosophic one. In order to complete the reaction, another thinker had to appear, and subject the whole science to a critical examination fitted to satisfy the deeper philosophic mind of the times. It is a curious circumstance that Hamilton uttered his first oracular declarations on Logic in a severe article on Whately, in the Edinburgh Meviezv, published afterwards in his Discussions. He embraced the opportunity to bring forth the result of his profound researches, and specially to introduce to the English speaking countries, the Logic which had sprung up in Germany out of

PREFACE. V

Kant's Critick of Pure Reason. Since that date, Logic has had a greater amount of interest collected round it in Great Britain than any other mental science, and has become incorporated with the freshest and brightest thought of the country. The interest in the study has been increased by the Logic of Mr. John Stuart Mill, who has evidently felt the influence of Whately in the respect which he pays to Formal Logic, but adheres, as a whole, to the principles of his father, Mr. James Mill, introducing some elements from the cognate Positive Philosophy of M. Comte. Mr. Mill has given an impulse to the study, not by the portion of his work which treats of Formal Logic — which is not of much scientific value — but by his valuable exposition of the Logic of Induction, which would have been of much more value had he left out the constant defences of his empirical metaphysics.

The New Analytic proceeds directly or indirectly from the metaphysics of Kant. Not that it is to be found developed in the works of Kant, but it is largely grounded on the peculiar principles of the Critioh of Pure Reason ; it rose out of the searching criticism to which Kant had subjected the forms of the Old Logic ; and it ramified directly from the logical treatises of such men as Krug and Esser who belonged to the school. It is of a composite structure, resembling the renovations we see in Britain of mediaeval buildings, the old and the new adapted to each other with wonderful skill, but with an occasional incongruity forcing itself here and there on the notice of the careful observer. I am not convinced that all the parts are likely to be preserved in the shape they now have, or vi PREFACE.

that the Analytic always gives the ultimate expression of the laws of thought ; but I am sure it is a valuable accession to the science. Altogether independent of its positive improvements, it has done great service, by the careful examination to which it has subjected the Old Logic — which has come creditably out of the trial. Forms which had become venerable, and, I may add, stiff, from age ; and which were inclined to stand on their dignity and acknowledged authority, have been obliged to submit to a sifting scrutiny, which may have shorn them of some of their ridiculous pretensions, but has, at the same time, delivered them from the dry dust which had gathered around them and threatened to bury them. The time has now come for subjecting the New Analytic to a like examination. It has been before us for an age in a half developed form, and for half an age in a fully unfolded shape ; and we should now be in a sufficiently impartial position to be able to take from it what is worthy of being retained, and to lay aside what is fallacious or mistaken.*

The defects and errors of the new Logic are derived mainly from its German paternity. It is infected throughout with the metaphysics of Kant — just as the Art of Thinking is with the metaphysics of Descartes, and Mill's Logic with the empiricism of Comte. It ever presupposes, or implies, that there are Forms in the mind which it imposes on objects as it contemplates them ; and it makes the science altogether a priori, and to be constructed apart from,

* I believe copies may be had of a limited edition of Philosophic Papers pub lished by me, and in which I examined Hamilton's Logic. 1 have reviewed Mill's Logic in my Examination of Mr. J. S, Mill's Philosophy.

PREFACE. vii

and altogether independent of experience. Hamilton quotes (Logic, Led. IV.) Esser with approbation. " It is evident that in so far as a form of thought is necessary, this form must be determined or necessitated by the nature of the thinking subject itself. . . . The first condition of a form of thought is that it is subjectively, not objectively, determined." This fundamental error (so I reckon it) runs through the whole system, and injures and corrupts the valuable truth to be found in the Logic of Hamilton. \ I acknowledge that there are principles or laws in the mind, original and native ; but these do not superinduce or impose forms on objects as we look at them ; they simply enable us to perceive what is in the objects. \ True, there are a priori laws in the mind operating prior to experience ; but we can discover their nature, and give an accurate expression of them, only by means of careful observation. The science of Logic is to be constructed only by a careful inductive investigation of the operations of the human mind as it is employed in thinking.

In conducting my independent researches in this spirit, I have been thrown back on the old Logic more than even the logicians of the school of Kant have been. But I have been obliged, in order to explain certain operations of thought to which Kant and Hamilton have called attention, to unfold laws which were not noticed by the older logicians.

The main feature of this Logical Treatise is to be found in the more thorough investigation of the nature of the Notion, in regard to which the views of the school of Locke and Whately are very defective, and the views of the school of Kant and Hamilviil PREFACE.

ton altogether erroneous. The Port Royal Logic complains that the part of Logic which comprehends the rules of reasoning is regarded as the most important ; and maintains that the greater part of the errors of men arises from their reasoning on wrongprinciples, rather than from their reasoning wrongly from their principles. It is as true of this age as of the seventeenth century, that the attention of logicians has been confined almost entirely to Reasoning. I believe that it is the Notion which requires at this time to be specially examined. I believe that errors spring far more frequently from obscure, inadequate, indistinct, and confused Notions, and from not placing the Notions in their proper relation in Judgment, than from Ratiocination. Even in Reasoning, most mistakes proceed from confusion lurking in the Apprehensions of the mind. We are in more need, at present, of a new analysis of the Notion and the Judgment, than of the Reasoning process. I have found that in the more thorough evolution of the nature of the Notion, especially in the thorough-going separation of the Abstract Notion from the Singular and Universal, we have the means of settling the curious questions which have been started in regard to Judgment and Reasoning in the New Analytic. In this treatise, the Notion (with the Term, and the Relation of Thought to Language) will be found to occupy a larger relative place than in any logical work written since the time of the famous Art of Thinking.

Princeton, New Jersey, U. S., April, 1S70.

Preface To Revised Edition

Much more attention is now paid to Logic than for several years prior to the time when I published this work. It is now seen that Formal Logic is the most certain science next to Geometry, and is more eminently fitted than any other branch of study to give accuracy to thinking. It is especially needed in the present day, when there is so much largeness, but at the same time so much looseness of thinking, which is to be restrained and corrected by the science which treats of the precise nature of thought.

It is well known that our science consists of Simple Apprehension, Judgment, and Reasoning, or, in other words, of the Notion, the Proposition, and the Argument. I am confirmed in the opinion that in the present day, of the three Parts, that most needing to be expounded is Apprehension or the Notion. Upon this the Judgment and the Reasoning largely depend. Error in thinking proceeds much more frequently and extensively from inadequate and confused Notions than from mistaken judgments and reasoning. More than one half of erroneous propositions and arguments spring from misapprehension and looseness in our ideas. I have, therefore, taken immense pains to

X PREFACE.

explain the nature of the various kinds of Notions, and to furnish a correct analysis and division of them. I have explained the relation of Language to Thought.

I may mention some other peculiarities of this treatise : —

Under Judgment I have explained the distinction between Substitutive (Convertible) and Attributive (Inconvertible) Judgments, and have given a full exposition of Implied Judgments or Immediate Inferences.

Under Reasoning I have enunciated the Regulating Laws of all ratiocination.

In closing, I have unfolded the Fundamental Principles which underlie Discursive Thought. I have appended exercises to help us to secure accurate thinking.

I have excluded the process of Induction from Formal Logic, that it may be placed under the separate head of Inductive Logic. But I have shown that there is Reasoning involved in rising from the scattered observed facts to the law, and how the Reasoning may be put in syllogistic form.

The tendency of German thinkers from the days of Hegel has been to extend the province of Logic, and to make it embrace the theory of knowledge and much that is properly metaphysical. I think it of vast moment to restrict it to its own field, which is that of Discursive Thought, and thus keep one great science, established by Aristotle, from endless speculation.

Princeton, N, J., May, 1891.

Table Of Contents

INTRODUCTION,

SUCTION PAGB

t— 5.— Definition of Logic 1

6 — 7.— Division of the Science 2

FOEMAL LOGIC. 8— 11.— The Notion, Judgment, and Eeasoning 4

Part First. The Notion

1.— Definition of Notion 1

2.— The Term ?

3. — All Notions either Concrete or Abstract 8

CONCRETE AND ABSTRACT NOTIONS.

4 — 6. — Nature of Concrete and Abstract Notions 8

7.— The Phantasy ... 10

8 — 9. — Abstractions from Concretes and other Abstractions 10

10.— Comprehension of Abstract Notions 12

LAWS OF THOUGHT INVOLVED IN ABSTRACTION.

11.— The Abstract implies the Concrete 12

12.— When tlie Concrete is Real the Abstract is Real 13

13.— An Attribute has no Independent Existence 14

14.— The Reality in the Abstract Notion 15

IS — 17.7^Importance of Abstraction 16

SINGULAR AND UNIVERSAL NOTIONS.

18.— All Notions either Singular or Universal 18

19,— Our Primary Knowledge is of Singulars 18

Xll

Contents

SECTION TAOB

20— 21.— Abstraction and Generalization not the same 19

22.— What is presupposed in Generalization 20

Part Second. Judgment

1.— Definition of Judgment <J8

CATEGORICAL PROPOSITIONS.

-Subject, Copula, and Predicate 93

—Nature of the Copula 94

— Modals 98

—In Quality, either Affirmative or Negative........ 95

—In Quantity, either Universal or Particular 95

Meaning of words 'All' and 'Some' 96

Indefinite or Indesignate Propositions . ... 98

CONTENTS. xv

SECTION PAGE

9. -Fourfold Division of Propositions, A, E, I, O 96

10.— Distribution of Terms 96

11.— Distribution of Subject and Predicate 97

18— 13.— Various Eelations between Subject and Predicate 97

14.— Equivalent Propositions 98

15.— Propositions in which the Relation is op Extension and

Comprehension 99

16. — Inconvertible and Convertible — Substitutive and Attributive 100

17— 18.— Difference between these 100

19— 20.— Cases in which Predicate is a General Notion Distributed (U) 101

21. — Predicables of Aristotle and Porphyry 109

22.— Should the Predicate always be Quantified ? 103

23.— Hamilton's Table of Judgments 104

CONJUNCTIONS OF PROPOSITIONS, CONDITIONALS, AND DISJUNC- TIVES.

24.— Various Conjunctions 105

25. — Conditionals and Disjunctives 10B

26.— Conditionals, their Nature 106

•-J7— 28.— Antecedent. Consequent, and Consequence 106

29. — Conditionals may be Equivalent or Attributive 107

80— 31.— Disjunctives, their Nature 107

IMPLIED JUDGMENTS, OR IMMEDIATE INFERENCES.

82.— Their Nature 108

33.— Conversion 108

34. — Opposition in Equivalent Propositions 109

35.— Opposition in Attributive Propositions 109

SQ.—Subalternation 110

37. — Contrary Opposition Ill

38.— Contradictory Ill

^.—Demonstration 112

40. — In discussion Propositions put as Contradictories 112

41.— Transposed Propositions obtained by Opposition 113

42. — Transposed Judgments obtained by Extension 114

43. — These not applicable to Equivalent Propositions 114

44. — The Interpretation, of Judgments gives Implied Propositions... 114

45.— Implied Judgments are obtained by Comprehension 116

The Interpretation of Marks 115

46.— Added Maries 115

47.— Added Subject and Predicate 115

48. — Summation of Predicates 115

49. — Privative Conceptions , 115

50.— Conditional Propositions 117

Si.— Disjunctive Propositions 117

52.— Rule as to Distribution of Terms in Implied Judgments 117

53. — Implied Judgments obtained from " men are responsible " 117

54.— How Logic aids in Determining the Truth of a Proposition 118 xvi CONTENTS.

Part Third. Reasoning

MOTION VABl

1. — The Process in the mind when we reason 120

2. — The Sameness of the Process 121

3. — Importance of Analyzing the Process 121

4.— Difference between Judgment Proper and Reasoning 122

5.— Involves Three Propositions. The Syllogism 123

6. — Syllogistic Analysis made by Aristotle 123

7.— Cannot reason from One Judgment. Enthymeme 123

8.— Extremes and Middle ; Premisses and Conclusion 124

RULES APPLICABLE TO EVERT KIND OF REASONING.

9.— (1) There should be only Three Terms 125

10— (2) And only one Middle 135

11. — (3) One Premiss must be Affirmative 125

12. — (4) If either Premiss Negative, the Conclusion Negative 125

13.— (5) To prove a Negative, one Premiss must be Negative 125

14. — What are the Regulating Principles of Reasoning ? 125

15.— First Regulating Principle. " Notions Equivalent to one and

the same third Notion equivalent to one another." 126

16.— The TJnfigured Syllogism of Hamilton 127

17.— Second Regulating Principle. " Whatever is predicated of a

Class, may be Predicated of the Members of the Class." 127

18.— Major and Minor Terms. Major and Minor Premisses 128

19.— Rules derived from the Dictum of Aristotle ; being

EULES APPLICABLE TO REASONING IN EXTENSION.

20.— (1) Middle Term distributed once 128

21. — (2) Term distributed in Conclusion only when in Premisses 12h

23.— (3) From two Particular Premisses no Conclusion 129

23.— (4) K one Premias Particular, Conclusion Particular 130

24.— These Rules apply only to cases in which there is a Concept 130

28— 29.— First Figure.— Its Special Rules 131

30— 31.— Second Figure.— Its Special Rules 132

32— 33.— Third Figure.— Its Special Rules 132

34— 35.— Fourth Figure.— Is it allowable? 133

36.— Mnemonic Lines 134

37.— Reduction 134

38.— Made by Implied Judgments 135

39. — Ostensive Reduction 135

40.— Reductio per lmpossibile 136

41 . —Immediate Inferences in Mediate Reasoning 137

12 — 44.— Reasoning in Comprehension 13*

CONTENTS. xvii

SUCTION PAGE

45.— The Two Dicta Combined ; 140

46.— Hamilton"s Table of Forms of Seasoning 141

47. — Mill's Theory of Reasoning Process 143

48 — Reasoning from Plurative Judgments 144

CONDITIONAL REASONING.

49. — Its Nature and Rules 145

60.— Common Forms 146

51— 63.— Relation of Conditional to Categorical Reasoning 146

DISJUNCTIVE REASONING.

54.— Its Nature and Rules 148

55.— Its Principal Forms 149

56.— Can be Reduced to Categorical 149

DILEMMA.

58.— Its Principal Forms 151

59.— A Trilemma, etc 151

60. — Reduction to Categorical Form 151

CHAINS OF REASONING, SORITES.

61.— Prosyllogism and Episyllogism 152

62.— Sorites 153

63.— Reduced to Series of Syllogisms 153

GENERAL REMARKS ON REASONING PROCESS.

64.— We get tbe Premisses from Intuition and Observation 155

65.— Individual and Combined Observation 155

66.— Some of the Observational Maxims written out, others not 156

67. — Some of them Certain, others only Probable 157

68.— Demonstration, in which the new steps are Intuitive 157

69.— Experiential or Probable Evidence 158

70.— Is all that can be had in Practical Matters 160

71.— Falls under the Dictum of Aristotle, and needs a Major Premiss. . 161

72 -73. — Reasoning Involved in Induction ; the Canons of Induction ; the

Major Premiss 161

74. — When Premisses only Probably True 16?

75— 76.— Concurrence of Evidence 165

77.— Whence the Rapidity of Reasoning Process ? r. . . 166

78.— In what sense are the Truths reached New ? 168 xviii CONTENTS.

SECTION PAOB

FALLACIES.

79. —Definition of Fallacy 169

80.— What Logic can do in guarding against Fallacies 169

8< -How the Heart sways the Head 171

82.— Division of Fallacies , 172

83.— Formal Fallacies 172

Undistributed Middle 178

84.— Elicit Process of Major or Minor Term 173

85.— Negative Premisses 174

86.— Arguments with more than Three Terms 174

87.— Fallacies of Conditionals. . 175

88.— Material Fallacies 175

88— 90.— Ambiguous Terms, especially Ambiguous Middle 175

91. — Fallacia Accidentis 178

92.— Equivocation 179

93.— Oblique Expression 180

94.— Fallacies of Confusion 180

95.— Fallacy of Division and Composition 181

96. — Imperfect Division 182

97.— Fallacy of Shifting Ground 183

98.— Fallacia Plurium Interrogationum 184

99.— Petitio Principii 184

100.— Syllogistic Seasoning not Petitio Principii 185

101.— Arguing in a Circle 185

102.— Ignoratio Elenchi 186

103.— Proving only part of the Question 187

104.— Fallacy of Objections 187

105.— Argumentum ad Hominem 187

106.— Argumentum ad Populum 188

107.— Argumentum ad Verecundiam 188

108.— Argumentum ad Ignorantiam 188

109.— Fallacy of Pretension 189

110. — Argument from Consequences 189

111.— Mistakes as to Onus Probandi 190

112.— Fallacies of Analogy 191

113.— Imperfect Enumeration 192

14.— Non Causa pro Causa 193

15.— Post Hoc ergo Propter Hoc 193

16.— Mistaking Sign for Cause 194

17.— Causa Essendi and Causa Cognoscendi ; Reason and Cause 194

FUNDAMENTAL LAWS OF DISCURSIVE THOUGHT.

118. — How they are discovered 195

119— The Law of Identity 195

120.— The Law of Contradiction 196

121 .-The Law of Excluded Middle 196

122.— The Principle of Equality 196

CONTENTS. X! X

SECTION PASB

123.— The Dictum of Aristotle 19ti

124.— The Principle of Attribution 197

125.— The Law of Division 197

126. —The Principle of Whole and Parts 198

127.— The Consideration of these belongs to Metaphysics 198

Appendix

I.— Exercises as to Forms

II. — Exercises as to Violations of Laws of Thought

27— 31— In Notions 207

82— 35.— In Judgments . 209

86— 68.— In Reasoning 909

Introduction

DEFINITION AND DIVISION OF THE SCIENCE.

1, Logic may be defined as the Science of the Laws ol Discursive Thought. The matter about -which it is employed lies in the mind : it is Thought, which is an exercise of the understanding, the intelligence, or the intellectual or cognitive powers, as distinguished from operations of the motive faculties such as emotion, moral perception or volition. Thought or intelligence may be of two "kinds. In some cases we perceive the object or truth at once : as when we see or touch the table before us, as when we know that the shortest distance between two points is a straight line. In other exercises we perceive the thing or truth by a process : from something given we draw something else, as when we argue from certain appearances in the sky that it will be rain, or from the structure of certain strata of the earth's surface that they have been formed in water. This second kind of thought is called Discursive, in which we proceed from something allowed to something else derived from it by thinking ; as distinguished from Intuitive Thought, in which we discern the truth immediately. The science which treats of the intuitive operations of the mind is called Metaphysics ; the science which considers the discursive acts is Logic.

2. The discursive operations, like all other agencies in nature, proceed in a regular manner, that is, according to laws. By carefully observing the acts of the mind in

2 INTRODUCTION.

thinking, we may discover what these laws are, and ex. press them in language or in formulae. In doing this, we are constructing a science, which is co-ordinated knowledge, as distinguished from the knowledge of individual things as they present themselves. As Logic co-ordinates what it observes, it is a science ; it is the science of the laws of discursive thought.

3. There is no definition of Logic" in any of the extant writings of Aristotle the founder of the science. Of later logicians some have given a narrower and some a wider definition than that adopted in the text. Some represent it as a pure science ; some as a mere art. Some, such as Whately, would have it treat of Seasoning exclusively (omitting the Notion and Judgment), while others would enlarge it so as to make it embrace all intelligence. The definition of the text gives it a rigidly exact field, while it comprises all the mental operations embraced under the laws of discursive thought.

4. It should be noted that Logic does not profess to impart to man the power of thinking any more than Grammar gives him the capacity of speech. Logic finds men engaged in apprehending, judging, and reasoning, and it seeks to unfold the laws involved, just as Grammar presupposes that men can speak, and proceeds to detect the rules of correct speech. And as Grammar by its rules enables persons to express themselves accurately, so Logic by expounding the laws of thought guards against mistakes in thinking. So far as Logic unfolds the laws of a department of our nature it is a science; so far as it supplies rules to guide and guard us in our discursive operations it is an art.

5. As Logic deals with Thought primarily, and looks at Language only secondarily and incidentally, it is thus easily distinguished from Grammar, Ehetoric, and the Science of Language, which all treat of speech, writing or language generally.

0. Discursive Thought may be viewed in its general aspects or in its more special applications. It may be contemplated as directed to objects of any kind, no

DEFINITION OF THE SCIENCE. 3

matter what they be, within or without us ; or it may be considered as looking to certain classes of objects ; thus it is evident that thinking is somewhat differently employed in mathematical demonstration from what it is when arranging objects in natural history. This gives us the grand division of the science. So far as it treats of discursive operations, whatever be the objects about which it is employed, it is called Universal or more commonly Formal Logic. So far as it considers thinking as lirected to special kinds of objects, it has been called Particular Logic or might be called Objective Logic ; it embraces such subjects as Demonstration and Induction. This work takes up the former of these.

7. Kant says, " Logic maybe considered as two- fold : as Logic of the general (universal) or the particular use of the understanding. The first contains the absolutely necessary laws of thought, without which no use whatever of the understanding is possible, and gives laws therefore to the understanding, without regard to the difference of objects on which it may be employed. The Logic of the particular use of the understanding contains the laws of correct thinking upon a particular class of objects. The former may be called elemental logic ; the latter the organon of this or that particular science. The latter is for the most part employed in the schools as a propaedeutic to the sciences, although, indeed, according to the course of human reason, it is the last thing we arrive at, when the science has been already matured and needs only the finishing touches towards its correction and completion; for our knowledge of the objects of our attempted science must be tolerably extensive and complete before we can indicate the laws by which a science of these objects can be established. General Logic is again either pure or applied. In the former, we extract all the empirical conditions under which the understanding is exercised, for example the influence of the senses, the laws of the memory, the force of habit, of inclination, consequently also the sources of prejudice, &c." He tells us, General Logic " makes abstraction of all content of cognition, that is of all relation of cognition to its object, and regards only the logical form in the relation of cognitions to each other, that is the form of thought in general." (Critique of Pure Reason, Part II., Meiklejohn's Trans lation.) The distinction between Universal and Particular Logic is

4 INTRODUCTION.

adopted in the text, but with an important modification. Kant makes Universal Logic look at thought apart altogether from content or objects, and supposes that the mind has laws or forms which it imposes on objects. In the text it is supposed that the laws of thought are the laws of the understanding in contemplating objects. Formal or Universal Logic treats of thought, not apart from content, out whatever be the content, that is, whatever be the objects.

UNIVERSAL OR FORMAL LOGIC.

8* Let us look at some of the common exercises of Discursive Thought. We have before us a piece of ice. So far as we simply look at it, and perceive its form and color, there is no discursive thought. But we can distinguish between its form and color, or we may think of its qualities, say, its coldness, its brittleness, its transparency ; we are now exercising thought upon the object perceived. The mere bodily senses can draw no such distinction. I can not by the eye separate the shape of the piece of ice from its transparency. But on the bare inspection of the object the mind can distinguish between it and any of its properties, or between one property and another. This is Abstraction, a simple and elementary exercise of discursive thought.

0. Again, on looking at two or more objects, we may notice that they resemble each other. An inhabitant of a northern country is travelling for the first time in a southern clime, and beholds a plant such as never fell under his view before, a plant with a leaf like a fan, and on going a little farther he notices another plant of much the same general form. Already he is exercising discursive thought. He was not doing so as long as he was a mere passive recipient of the impression left on the eye by the shape and color ; but when he discovers the likeness of the plants he is exercising what is called Com-

DIVISION OF THE SCIENCE. 5

parisou. As other like plants fall under his view, he will probably take a farther step ; he will form a class 01 kind which shall embrace not only the plants which he has seen, but all others, with the points of agreement, . which may fall under his notice or that of any other man ; and he will rejoice if some one gives him the name of ' fan palm ' to designate them.