Psychical elements constituting the concept.—Experiential origin of the idea of cause: different solutions have all a common basis.—Its primitive individual character. Its extension.—Subjective and anthropomorphic period of generic images.—Period of reflexion, partial elimination of its subjective character, reduction to an invariable relation.—The notion of universal causality is acquired and remains a postulate.—Two ideas have hindered the development of this last notion: that of miracles and that of chance.—Transformation of the notion of cause. Rule of scientific research: its position is exterior. Identity of cause and effect.—Present form of the principle of universal causality.—Two quite distinct notions of cause (force, invariable relation), one of which is alone a concept 180 _Section V.—The Concept of Law._ Objective value of general ideas. Two contrary theories. Mere approximations to the psychologist.—Three periods in the development of the notion of law.—Period of generic images. Primitive sense of the word law.—Period of empirical laws, corresponding with the intermediate forms of abstraction. Characteristics: identity of fact and law; complexity.—Period of theoretical or ideal laws, corresponding to medium forms of abstraction. Its features: simplicity, quantitative determination, ideal formula 194 _Section VI.—The Concept of Species._ Its value: contemporaneous discussion of this subject. Component elements of the concept of species: resemblance, filiation. Difficulties resulting from polymorphism, from alternate generation.—Races, varieties.—Temporary and provisional objectivity.—Genera. Theories of Linnæus and Agassiz.—Shifting character of the classifications above the species.—One common point between transformists and their opponents: practical value of concepts. Not realities, nor fictions, but approximations.—Laws and species dependent on conditions of existence and varying with them 203 CHAPTER VI. CONCLUSION. How was the faculty of abstracting and of generalising constituted? Two principal causes: utility, appearance of inventors.—How has it developed? Three principal directions: practical, speculative, scientific.—_Résumé_: necessary co-operation of two factors: the one conscious, the other unconscious 216 CHAPTER I. THE LOWER FORMS OF ABSTRACTION. ABSTRACTION PRIOR TO SPEECH.