 The Autobiography, written at a time when Avicenna had reached his philosophical maturity, touches upon a number of issues that he felt were highly significant in his formation as a thinker and accordingly point the way to his approach to philosophy and his philosophical aims and orientation. These were, first, his understanding of the structure of philosophical knowledge (all intellectual knowledge, that is) as a unified whole, which is reflected in the classification of the sciences he studied; second, his critical evaluation of all past science and philosophy, as represented in his assessment of the achievements and shortcomings of previous philosophers after he had read their books in the Samanid library, which led to the realization that philosophy must be updated; and third, his emphasis on having been an autodidact points to the human capability of acquiring the highest knowledge rationally by oneself, and leads to a comprehensive study of all functions of the rational soul and how it acquires knowledge (epistemology) as well as to an inquiry into its origins, destination, activities, and their consequences (eschatology). Accordingly Avicenna set himself the task of presenting and writing about philosophy as an integral whole and not piecemeal and occasionalistically; bringing philosophy up to date; and studying how the human soul (intellect) knows as the foundation of his theory of knowledge, logical methodology, and the relation between the celestial and terrestrial realms, or the divine and human. 