There is a complex relationship between sociology and psychology, specifically social psychology. Social psychology should not be confused with sociology. While sociology depends on psychological principles, it remains distinct from (social) psychology. The idea that social phenomena like language, law, and culture possess a collective psychological reality independent of individuals, has to be critiqued.

Collective behaviors such as crowds acting in unison are often misinterpreted as resulting from a collective mind rather than individual psychological processes influenced by social interaction. But the observable uniformity of collective actions are different from the individual psychological processes that are involved. Social environments have an impact on individual psychology; individuals' behaviors and mental processes can change when influenced by a group. But these changes remain rooted in individual psychology; they don’t require the postulation of a supra-individual psychological entity.

Statistical and ethnological descriptions of social phenomena often mistakenly attribute social or psychological significance to mere numerical similarities among individuals. Social psychology should focus on how individual psychological processes are modified through social interaction, thus situating it as a subset of individual psychology rather than a separate field.

So, the distinction between sociology and psychology should be maintained, while recognizing their interdependence.

Source:

Simmel, G. (1908), Exkurs über Sozialpsychologie, in: Soziologie - Untersuchungen über die Formen der Vergesellschaftung, p. 556 — 563, Leipzig: Duncker & Humblot.