  We address the problem of the energy conditions in modified gravity taking
into account the additional degrees of freedom related to scalar fields and
curvature invariants. The latter are usually interpreted as generalized {\it
geometrical fluids} that differ in meaning with respect to the matter fluids
generally considered as sources of the field equations. In extended gravity
theories the curvature terms are encapsulated in a tensor $H^{ab}$ and a
coupling $g(\Psi^i)$ that can be recast as effective Einstein field equations,
with corrections to the energy-momentum tensor of matter. The formal validity
of standard energy inequalities does not assure basic requirements such as the
attractive nature of gravity, so we argue that the energy conditions have to be
considered in a wider sense.
