Introduction PART ONE: PRIMARY EFFECTS I PRIMARY ILLUSIONS AND THE LAW OF RELATIVE CENTRA TIONS II EFFECTS OF CENTRA TION PART TWO: PERCEPTUAL ACTIVITIES III PERCEPTUAL ACTIVITIES AND SECONDARY ILLUSIONS IV PERCEPTUAL CONSTANCIES AND CAUSALITY V PERCEPTIONS OF MOVEMENT, OF VELOCITY AND OF TIME PART THREE: STRUCTURES OF PERCEPTION AND OF INTELLIGENCE VI DIFFERENCES, SIMILARITIES AND POSSIBLE FILIATIONS BETWEEN THE STRUCTURES OF PERCEPTION AND THOSE OF INTELLIGENCE VII THE PERCEPTUAL OR NON-PERCEPTUAL ORIGINS OF THE STRUCTURES OF INTELLIGENCE VIII CONCLUSION: THE EPISTEMOLOGY OF PERCEPTION