Psychologists often write theoretical papers in which they propose their own theories or extend existing theories about a research problem in the field. For example, in one journal article, a psychologist argues that the field needs to combine attachment theory and social network theory to understand child and adolescent development.
If you are asked to write a theoretical paper for a course, you will be expected to support the theory you propose by pointing to evidence and counterevidence from the literature in the field, to compare your theory with others, and possibly to suggest experiments that could test your theory more rigorously.
Related topics:
Literature reviews
Research papers
Poster presentations