Historical Philosophy . . .
One thinks of philosophers such as Socrates, Plato, Aristotle.
Can a form exist without any instances of the object? For example, can there be such a thing as apple-ness if there are no apples? Many mythological creatures never existed (but they are based on composites of real creatures).
The problem with studying the soul is when you try to analyze it too deeply, too scientifically, you get nowhere. The best we can do is to describe it and provide helpful and practical advice for how to live, how to structure society.
The Social Sciences attempt to study the soul but they are descriptive sciences, not experimental sciences. But there are many interesting observations with practical benefits (such as psychological therapies based on Behavorism).
The system of philosophy developed by Aristotle and Aquinas seems much too complex and arbitrary to me. Certainly the various designations such as intellect, will, form, accidents, etc., seem useful as aids to thinking, but the whole system doesn't explain or match reality very well. It seems that the soul is not really as they describe it.
There is an abundance of useful information from the study of psychology. But psychology is based on materialistic assumptions which are simply not true. For example, Behavorism assumes that people don't have free will, and Freud taught that God is merely a projection of our desires.
Psychological studies and theories have spawned people's thinking and the experimental side is certainly useful. There are practical therapies for certain symptoms which seem to work sometimes (even though the theoretical underpinnings are flawed).