As a philosophy of the subject, modern thought has been characterized as a whole. This distinction is owed to the audacious hope that the subject could serve as the ultimate principle of the foundation of knowledge. However, the interest in clarifying its structure has been pushed into the background. This structure is at the center of Manfred Frank's latest book, which offers a look at the modern history of subject theories, combining analyses of the inner nature and temporality of the subject with its relationship to intersubjectivity and a discussion of classical and contemporary analytical theories. The concept of self-knowledge plays a key role in this context.