In this article we examine the contribution to the analysis of the pro
blem of internalization made by the Russian psychologist Gal'perin. Th
e concept of internalization has been criticized recently for restrict
ing researchers to an old paradigm of Cartesian dualism, with the sugg
estion made that clearer concepts such as mastery or appropriation be
substituted. In our view, the concept of internalization has the advan
tage of pointing to a specifically human type of appropriation. We pro
pose an alternative solution. Rather than replacing one term with anot
her, the very notions of internal and external in the realm of mental
activity should be reconceptualized. In the framework of Gal'perin's i
deas, the processes underlying the internalization concept can be cons
trued without creating dualistic confusion. The result is a better und
erstanding of the specificity of human mental development.