  In this paper, we deal with the notions of naturality from category theory
and definablity from model theory and their interactions. In this regard, we
present three results. First, we show, under some mild conditions, that
naturality implies definablity. Second, by using the reverse Easton iteration
of Cohen forcing notions, we construct a transitive model of ZFC in which every
uniformisable construction is weakly natural. Finally, we show that if F is a
natural construction on a class K of structures which is represented by some
formula, then it is uniformly definable without any extra parameters. Our
results answer some questions by Hodges and Shelah.
