  We discuss the non-adiabatic or entropy perturbation, which controls the
evolution of the curvature perturbation in the uniform density gauge, for a
scalar field system minimally coupled to gravity with non-canonical action. We
highlight the differences between the sound and the phase speed in these
systems, and show that the non-adiabatic pressure perturbation vanishes in the
single field case, resulting in the conservation of the curvature perturbation
on large scales.
