  Temporal logics are extensively used for the specification of on-going
behaviours of reactive systems. Two significant developments in this area are
the extension of traditional temporal logics with modalities that enable the
specification of on-going strategic behaviours in multi-agent systems, and the
transition of temporal logics to a quantitative setting, where different
satisfaction values enable the specifier to formalise concepts such as
certainty or quality. We introduce and study FSL---a quantitative extension of
SL (Strategy Logic), one of the most natural and expressive logics describing
strategic behaviours. The satisfaction value of an FSL formula is a real value
in [0,1], reflecting `how much' or `how well' the strategic on-going objectives
of the underlying agents are satisfied. We demonstrate the applications of FSL
in quantitative reasoning about multi-agent systems, by showing how it can
express concepts of stability in multi-agent systems, and how it generalises
some fuzzy temporal logics. We also provide a model-checking algorithm for our
logic, based on a quantitative extension of Quantified CTL*.
