2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/194177We reconcile seemingly conflicting statements in the literature about the behavior of cosmological solutions in modified theories of gravity where the Einstein-Hilbert Lagrangian for gravity is modified by the addition of a function of the Ricci scalar, f(R). Using the example of f(R) = +/-μ^4/R we show that only such choices of f(R) where d^2f/dR^2>0 have stable high-curvature limits and well-behaved cosmological solutions with a proper era of matter domination. The remaining models enter a phase dominated by both matter and scalar kinetic energy where the scalar curvature remains low.4 pages, 2 figures, v2 reflects version accepted for publication in PRD: minor typos fixed and references updatedAstrophysicsGeneral Relativity and Quantum CosmologyHigh Energy Physics - Theorytext