The paper is concerned with generalized (i.\,e. monotone and possibly non-additive) measures. A discussion concerning the classification of these measures, according to the type and amount of non-additivity, is done. It is proved that $\lambda$-additive measures appear naturally as solutions of functional equations generated by the idea of (possible) non additivity.
generalized measure (probability), $\lambda $-additive measure, functional equation
28E05, 39B05, 60A86, 28A23, 28E10, 39B22