D Hilbert 
Principles of Mathematical Logic [PDF ebook] 

David Hilbert was particularly interested in the foundations of mathematics. Among many other things, he is famous for his attempt to axiomatize mathematics. This now classic text is his treatment of symbolic logic. This translation is based on the second German edition and has been modified according to the criticisms of Church and Quine. In particular, the authors’ original formulation of Goedel’s completeness proof for the predicate calculus has been updated. In the first half of the twentieth century, an important debate on the foundations of mathematics took place. Principles of Mathematical Logic represents one of Hilbert’s important contributions to that debate. Although symbolic logic has grown considerably in the subsequent decades, this book remains a classic.