A notion of nondeterministic inference on inexact information is intro
duced. The model is characterized by a second order probability distri
bution on beliefs together with an updating procedure. Such nondetermi
nistic inference processes naturally generate a corresponding determin
istic process which essentially involves calculating the expected resp
onse of the nondeterministic process. Given that the number of proposi
tional variables in the relevant language may vary, it is natural to c
onsider hierarchies of inference processes, these being characterized
by hierarchies of prior distributions. A number of logical principles
are considered which in the presence of certain smoothness assumptions
restrict the choice of hierarchies to hierarchies of symmetric Dirich
let priors where each prior is defined up to a parameter lambda which
is constant over the whole hierarchy A principle of maximal expected d
ependency between propositional variables is then introduced which res
tricts lambda to a particular value. (C) 1997 Elsevier Science Inc.