To these general conditions must be added the plain and everyday contrast between the metaphysical perfection of criminal law and the progressive increase of crime, as well as the contrast between legal theories of crime and the study of the mental characteristics of a large number of criminals.
Ferri disputed the emphasis on physiological characteristics of criminals; instead, he focused on the study of psychological characteristics, which he believed accounted for the development of crime in an individual. These characteristics included slang, handwriting, secret symbols, literature, and art, as well as moral insensibility.
INTRODUCTION. THE POSITIVE SCHOOL OF CRIMINAL LAW.
CHAPTER I. THE DATA OF CRIMINAL ANTHROPOLOGY.
CHAPTER II. THE DATA OF CRIMINAL STATISTICS.
CHAPTER III. PRACTICAL REFORMS.