Why did Auguste Comte exclude psychology as an independent science in his system?

Auguste Comte did not include psychology as an independent science in his system because he believed it should be subsumed under biology—specifically brain neurophysiology—and sociology.1

Comte’s exclusion of psychology was driven by his commitment to the scientific method and his skepticism regarding introspection. He argued that attempting to observe one's own mental states would inevitably alter and distort them, making the practice scientifically unreliable. By insisting on the necessity of objective observation, Comte anticipated the methodology later adopted by 20th-century behaviourism. In his hierarchical structure of the sciences, he viewed higher-level disciplines as dependent upon the knowledge provided by those below them, ultimately positioning sociology as the culmination of his positive philosophy.12