no ‘fine–tuning’.

In this paper we also consider scalar field cosmologies, but we shift the perspective from the usual interpretation of a scalar field [*source*]{} in Einstein’s equations to a mean field description of averaged inhomogeneities. We see a number of advantages entailed by such a description that motivated the present investigation. First, a (homogeneous) scalar field as a model of spatially averaged (i.e. effectively homogeneous) geometrical degrees of freedom that are physically present does not need to be justified as an additional source arising from fundamental field theories; it has a well–defined physical status and, as such, does not suffer from a phenomenological parameterization, since it is constrained by Einstein’s field equations. Second, inhomogeneities encoded in backreaction terms [*give rise to*]{} the scalar field cosmology, fixing its potential, its equation of state, etc.; they not only influence the evolution of the scalar field, but they determine it. Third, the proposed correspondence allows a realistic reinterpretation of quintessence models and other phenomenological approaches involving scalar fields. These approaches must not be considered as independent alternatives, they here describe the same physics that also underlies the backreaction approach, and so can be confronted with physical constraints; in other words, if backreaction 