I know this should be an easy question but I don't think it is:
What exactly is the difference between philosophy and psychology?
At one time, psychology was a branch of philosophy. Namely, the branch that dealt with questions concerning the nature of the soul. "Pyche" is the Greek word for soul so psychology was literally the study of the soul and it essential characteristics.
With the development of modern biology (the use of the microscope) and modern statistical methods, along with a more rigorous application of the scientific method, both biology and psychology broke away from philosophy (which is also known as "the queen of the sciences," and became well established scientific endeavors.
Philosophy still remains to examine matters regarding the true (logic and epistemology (theory of knowledge); the good (ethics); and the beautiful (aesthetics).