The problem which I have chosen is one which is common to metaphysics and psychology, the problem of free will. What I attempt to prove is that all discussion between the determinists and their opponents implies a previous confusion of duration with extensity, of succession with simultaneity, of quality with quantity: this confusion once dispelled, we may perhaps witness the disappearance of the objections raised against free will, of the definitions given of it, and, in a certain sense, of the problem of free will itself. To prove this is the object of the third part of the present volume: the first two chapters, which treat of the conceptions of intensity and duration, have been written as an introduction to the third. H. BERGSON. _February,_ 1888. CONTENTS CHAPTER I THE INTENSITY OF PSYCHIC STATES Quantitative differences applicable to magnitudes but not to intensities, 1-4; Attempt to estimate intensities by objective causes or atomic movements, 4-7; Different kinds of intensities, 7; Deep-seated psychic states: desire, 8, hope, 9, joy and sorrow, 10; Aesthetic feelings, 11-18: grace, 12, beauty, 14-18, music, poetry, art, 15-18; Moral feelings, pity, 19; Conscious states involving physical symptoms, 20: muscular effort, 21-26, attention and muscular tension, 27-28; Violent emotions, 29-31: rage, 29, fear, 30; Affective sensations, 32-39: pleasure and pain, 33-39, disgust, 36; Representative sensations, 39-60: and external causes, 42, sensation of sound, 43, intensity, pitch and muscular effort, 45-6, sensations of heat and cold, 46-7, sensations of pressure and weight, 47-50, sensation of light, 50-60, photometric experiments, 52-60, Delbœuf's experiments, 56-60; Psychophysics, 60-72: Weber and Fechner, 61-65, Delbœuf, 67-70, the mistake of regarding sensations as magnitudes, 70-72; Intensity in (1) representative, (2) affective states, intensity and multiplicity, 72-74. _pp._1-74 CHAPTER II THE MULTIPLICITY OF CONSCIOUS STATES THE IDEA OF DURATION