This book is about Early Heideggers philosophy, especially on his book Being and Time and some other books. In this study, we tried to explore Heideggers philosophy and discussed his philosophy by contrasting to Descartess ontology and epistemology. This study shows that Heidegger's "destruction" of the history of ontology with regard to Descartes' "cogito sum" does not mean "elimination" or annihilation, rather it is to be understood as "retrieval" and "reinterpretation" of the question Being; in this sense, Heidegger's critique of Descartes, his destruction of the history of ontology, and his existential analytic of the Being of Dasein contribute to the clarification of the meaning of Being. One of ur purpose is to discuss how the tra-ditional metaphysics, especially in Descartes' philosophy of ontology, covers the question of being concerning clear and distinct idea of cogito. The rethinking of Heideggers interpretion of technology and science has been explored, too. Starting with the eigth part, we discuss some other problems or subject in philosophy in general.