Franz Brentano (1838-1917) was a German philosopher and early psychologist, who was instrumental in developing psychology into an empirical science.
Brentano agreed with Wundt that psychology must be a scientific study of consciousness, based on empirical observation. But while Wundt’s psychology embraced an experimental approach, Brentano’s did not. According to Brentano, psychological studies should proceed mainly by observation, not by experimentation. Also, he identified the content of psychology as the mental activity of consciousness, rather than the structure of consciousness, as the Wundtian school believed. For example, the color of a flower is an attribute of the flower--that is, it is a physical quality. However, the experience of seeing the color is a mental quality or, as Brentano termed it, a mental activity or whole act. His model became known as Act Psychology. Brentano’s work influenced the later developments of Gestalt and Humanistic psychology.