Acknowledgments I would like to express my sincere gratitude to all the people who made the realization of this dissertation possible, particularly my advisor, Professor Ilan Tojerow, for his trust and his interesting topic suggestion, as well as Nathalie Sauze and Eric Vandevyver for their support and advices. Index Introduction 5 Part One: Accessibility in the literature 6 Chapter One: The concept of accessibility 7 Section 1: The four determining factors of accessibility 7 Section 2: Accessibility