  There are many Slowly Pulsating B (SPB) stars and gamma Dor stars in the
Kepler Mission data set. The light curves of these pulsating stars have been
classified phenomenologically into stars with symmetric light curves and with
asymmetric light curves. In the same effective temperature ranges as the gamma
Dor and SPB stars, there are variable stars with downward light curves that
have been conjectured to be caused by spots. Among these phenomenological
classes of stars, some show `frequency groups' in their amplitude spectra that
have not previously been understood. While it has been recognised that
nonlinear pulsation gives rise to combination frequencies in a Fourier
description of the light curves of these stars, such combination frequencies
have been considered to be a only a minor constituent of the amplitude spectra.
In this paper we unify the Fourier description of the light curves of these
groups of stars, showing that many of them can be understood in terms of only a
few base frequencies, which we attribute to g mode pulsations, and combination
frequencies, where sometimes a very large number of combination frequencies
dominate the amplitude spectra. The frequency groups seen in these stars are
thus tremendously simplified. We show observationally that the combination
frequencies can have amplitudes greater than the base frequency amplitudes, and
we show theoretically how this arises. Thus for some gamma Dor and SPB stars
combination frequencies can have the highest observed amplitudes. Among the B
stars are pulsating Be stars that show emission lines in their spectra from
occasional ejection of material into a circumstellar disk. Our analysis gives
strong support to the understanding of these pulsating Be stars as rapidly
rotating SPB stars, explained entirely by g mode pulsations.
