Language in animals.—The origin of speech; principal contemporaneous hypotheses; instinct, progressive evolution. The cry, vocalisation, articulation. Transitional forms: co-existence of speech and of the language of action; co-existence of speech and of inarticulate sounds.—The development of speech. Protoplasmic period without grammatical functions.—Roots; two theories: reality, and residue of analysis.—Did speech begin with words or with phrases?—Successive appearance of parts of speech. Adjectives or denominations of qualities. The substantive a contraction of the adjective. Verbs not a primitive phenomenon; the three degrees of abstraction.—Terms expressive of relations. Psychological nature of relation, may be reduced to change or movement. Function of analogy 54 CHAPTER III. INTERMEDIATE FORMS OF ABSTRACTION. Division into two classes according to the function of the word.—First class. Words not indispensable, and only in a limited degree the instrument of substitution.—Difference between generic images and lower concepts. Characteristics of these two classes. Is there continuity between the two? Nature of the lower forms of intermediate abstraction, according to languages, numeration, etc. Concrete-abstract period.—Second class. Words are indispensable and become an instrument of substitution.—Difficulty in finding examples.—History of zoölogical classification: pre-scientific period: Aristotle, Linnæus, Cuvier, etc., contemporary writers. Progress towards unity 86 CHAPTER IV. HIGHER FORMS OF ABSTRACTION. THEIR NATURE. Object of the chapter: What is there in consciousness, when we think by concepts?—The general idea as a psychical state may be reduced to varieties. Investigation of this point: the method pursued.—Reduction to three principal types. Concrete type the most widely distributed. Variation; reply by association of ideas. Visual typographic type: printed words seen and nothing further.—Auditory type; less common.—Interrogations by general propositions: same results. Investigation of cases in which words exist alone in consciousness. Is it possible to think with words only? Rôle of unconscious knowledge. General ideas are intellectual habits.—Natural antagonism between the image and the concept. Its causes.—Are there general ideas or merely general terms? 111 CHAPTER V. EVOLUTION OF THE PRINCIPAL CONCEPTS. _Section I.—The Concept of Number._