, V-IX, Moral obligation — Kant and J. Piaget, in , Sektionen V-IX, Freiburg-Basel-Wien, Herder, pp. 96-102.
, 1972a, Kant's attitude toward human perfection as a moral determinant, in L. White Beck (ed.), Proceedings of the Third international Kant congress, Dordrecht, Springer, pp. 339-345.