Because psychology is a diverse discipline PSYC majors are required to take (at least) two courses that approach the discipline through a more natural science focus and two that approach the discipline through a more social science focus. In each of these areas, one must be a "core" course, meaning it has a broad focus. The other can either be a core or an elective course with a designation in that area.
The core courses with a natural science focus are: PSYC 1300 Introduction to Cognitive Science, and PSYC 1600 The Human Brain.
The core courses with a social science focus are: PSYC 1400 Developmental Psychology, PSYC 1500 Social Psychology, and PYSC 1700 Clinical Psychology.
Elective courses very from semester to semester, so please consult courses.yale.edu.