Final answer:
To become a psychology professor at a 4-year college, one typically needs to obtain a PhD in psychology, following the initial completion of a bachelor's degree and a master's program.
Step-by-step explanation:
To become a psychology professor at a 4-year college, an individual would typically need to have a PhD in psychology. Starting with a bachelor's degree, either a Bachelor of Science (B.S.) or a Bachelor of Arts (B.A.), is the first step. However, teaching at the college level usually requires advanced studies beyond a bachelor's degree. After obtaining their bachelor's degree, one would typically pursue a graduate program, starting with a master's degree followed by a doctoral program. The most common degree for a college professor in psychology would be a Doctor of Philosophy (PhD) in psychology, as it provides the comprehensive education and research experience necessary for a career in academia.