Martin Heidegger 
Kant and the Problem of Metaphysics [PDF ebook] 

Whilst the greatest effort has been made to ensure the quality of this text, due to the historical nature of this content, in some rare cases there may be minor issues with legibility. As ontology is an inquiry concerned with the Being of things, so fundamental ontology is an inquiry concerned with the possibility of ontology. In other words, its object is the analysis of the comprehension of Being as that on which ontology itself depends; it is concerned to uncover the source of the objectivity factor as that without which objective experience would be impossible. If the first Critique is a laying of the foundation of ontology (metaphysics), this foundation being the comprehension of Being itself as that which makes ontology possible, then the Critique is ultimately concerned with the preparation of this foundation, i.e., with determining from what and in what manner this foundation itself arises.