This paper discusses the effects of omitting constraint modes corresponding to applied loads in systems modeled with component mode synthesis. A method of correcting for the omitted constraint modes is also developed. The free component mode synthesis method is applied to the continuous model of a axial rod-spring system, and the effect of omitted constraint modes on the static, steady state harmonic, and transient response is studied. The effect of omitted constraint modes on the transient response of an asymmetric beam is studied using the free and fixed component mode synthesis implemented in MSC/NASTRAN. A simple pinned truss finite element model is also studied.