Conflict and compromise formation are central aspects of mental life. They dispose to constant mental change. Limitations of knowability in psychoanalysis are inextricably connected with constant mental change — the latter sometimes diminishing unknowability and sometimes exacerbating it. This paper explores three kinds of unknowability in psychoanalysis and their relation to constant mental change. That relation clarifies to some degree the implications of certain controversial proposals for change in psychoanalytic theory, method, and technique.