The role of shear in determining the ideal MHD stability properties of tokamaks is discussed. In particular, we assess the effects of low shear within the plasma upon pressure-driven modes. The standard ballooning theory is shown to break down, as the shear ia reduced and the growth rate is shown to be an oscillatory function of n f the toroidal mode number, treated as a continuous parameter. The oscillations are shown to depend on both the pressure and safety-factor profiles. When the 3hear is sufficiently weak, the oscillations can result in bands of unstable n values which are present even when the standard ballooning theory predicts complete stability. These instabilities are named "infernal modes." The occurrence of. these Instabilities at integer n is shown to be a sensitive function of q-axis, raising the possibility of a sharp onset AS plasma parameters evolve. DISCLArMER