The fuzzy coalition game theory brings a more realistic tools for the mathe
matical modelling of the negotiation process and its results. In this paper
we limit our attention to the fuzzy extension of the simple model of coali
tion games with side-payments, and in the frame of this model we study one
of the elementary concepts of the coalition game theory, namely its "additi
vities", i.e., superadditivity, subadditivity and additivity in the strict
sense. In the deterministic game theory these additivites indicate the stru
cture of eventual cooperation, namely the extent of finally formed coalitio
ns, if the cooperation is possible. The additivities in fuzzy coalition gam
es play an analogous role. But the vagueness of the input data about the ex
pected coalitional incomes leads to consequently vague validity of the supe
radditivity, subadditivity and additivity. In this paper we formulate the m
odel of this vagueness depending on the fuzzy quantities describing the exp
ected coalitional pay-offs, and we introduce some elementary results mostly
determining the links between additivities in a deterministic coalition ga
me and its fuzzy extensions.