Gravity waves are known to propagate in the continuous as well as the partially and fully guided modes. Through the development of a dispersion formula we will show that these three modes can ''interfere'' among themselves and that one important consequence of such ''interference'' is that the guidance of a large number of partially guided modes can be destroyed. The simple formula for the effective attenuation distance, -1/Im kxn for each complex partially guided mode kxn (where kx is the horizontal wave vector), is no longer valid when there is heavy interference or ''model overlap.'' A simple criterion will be developed to distinguish those modes which remain observable from those which exist physically only as part of the general background. We will also show that the presence of an explicit gravity wave source can only selectively or simultaneously excite those modes which are observable and that the other modes remain as part of the background, unaffected by the source. The dispersion formula also shows that a discrete mode should be described by two parameters. One is the usual modal position kxn, while the other is the ''weight'' which varies with different modes. There is also the possible existence of yet another form of guided mode which we will call the virtually guided mode and which possesses characteristics quite different from the other guided modes.