The two branches of the APES for the case of strong PJTE resulting in the instability of the ground state (when the condition of instability (11) holds) are illustrated in Fig. 1b in comparison with the case when the two states have the same energy (Fig. 1a), i. e. when they are degenerate and the Jahn–Teller effect (JTE) takes place. We see that the two cases, degenerate and nondegenerate but close-in-energy (pseudo degenerate) are similar in generating two minima with distorted configurations, but there are important differences: while in the JTE there is a crossing of the two terms at the point of degeneracy (leading to conical intersections in more complicated cases), in the nondegenerate case with strong vibronic coupling there is an "avoided crossing" or "pseudo crossing". Even a more important difference between the two vibronic coupling effects emerges from the fact that the two interacting states in the JTE are components of the same symmetry type, whereas in the PJTE each of the two states may have any symmetry. For this reason, the possible kinds of distortion is very limited in the JTE, and unlimited in the PJTE. It is also noticeable that while the systems with JTE are limited by the condition of electron degeneracy, the applicability of the PJTE has no a priori limitations, as it includes also the cases of degeneracy. Even when the PJT coupling is weak and the inequality (11) does not hold, the PJTE is still significant in softening (lowering the corresponding vibrational frequency) of the ground state and increasing it in the excited state. When considering the PJTE in an excited state, all the higher in energy states destabilize it, while the lower ones stabilize it.