The objective of the book. Mathematical logic, which can be addressed in terms of its method as mathematics and in terms of its subject as logic, represents one of those fields of knowledge where the original interests of mathematicians and non-mathematically oriented scholars currently intersect. The regularity of thought has largely revealed itself to be of a kind similar to mathematical regularities, and no logic can ignore this fact any longer, just as no physics can ignore the analogous fact today. Accordingly, this book aims to address mathematicians initially, but also mathematically interested non-mathematicians, particularly those with a background in the humanities.