  In a recent paper, "Reexamining $f\left(R,T\right)$ gravity", by S. B. Fisher
and E. D. Carlson, Phys. Rev. D 100, 064059 (2019), the authors claim that for
the particular $f(R,T)$ modified gravity model, with $f(R,T)=f_1(R)+f_2(T)$,
the term $f_2(T)$ must be included in the matter Lagrangian and therefore it
does not have any physical significance. We carefully reexamine the line of
reasoning presented in the paper, and we show that there are several major
conceptual problems related to the author's physical interpretations, as well
as in the physical and mathematical approaches used to derive the
energy-momentum tensor of the theory. These problems raise some serious
concerns about the validity of most of the results presented in the paper.
