Comments on "Solar System constraints to general f(R) gravity"

We comment on, and complete, the analysis of the weak field limit of metric f(R) gravity in T. Chiba, T.L. Smith, and A.L. Erickcek, Phys. Rev. D 75, 124014 (2007).Comment: 2 latex pages, to appear in the Comments section of Phys. Rev. D. A statement corrected, acknowledgments update

Breakdown of the initial value formulation of scalar-tensor gravity and its physical meaning

We revisit singularities of two distinct kinds in the Cauchy problem of general scalar-tensor theories of gravity (previously discussed in the literature), and of metric and Palatini f(R) gravity, in both their Jordan and Einstein frame representations. Examples and toy models are used to shed light onto the problem and it is shown that, contrary to common lore, the two conformal frames are equivalent with respect to the initial value problem.Comment: 14 pages, LaTex, to appear in Phys. Rev.