This book is dedicated to the memory of Hughes Leblanc whose work was influential in many fields of philosophical logic, including especially truth-value (substitutional) semantics, probabilistic interpretations for classical and intuitionistic logic and natural deduction. In 1970, Hughes joined with 23 other philosophers and logicians attending a conference in Montréal to found the Society for Exact Philosophy. The papers collected in this volume derive from the program of the annual meeting of the Society for Exact Philosophy held at the Université de Montréal in 2001. All of the papers are in the spirit of Hughes' work: to explore and try to solve philosophical problems in a sound and systematic way, with the help of formal logico-mathematical tools.