One of the basics of learning criminology is understanding where it started. The earliest scholars in criminology were broken into three main ideologies: Classical, Chicago, and Positivist. During the 18th century through much of the 20th century, it was these three schools of thought that helped define the field- yet were eventually dismantled by modern studies in criminology. Today, other perspectives take the present and explore more diverse perspectives. Some examples include critical criminology, feminism and criminology, and social-based criminology.