Ultimate negation - The fourth type of abhāva (negation);
it is an eternal non-existence in a substance in the form of impossibility of transformation of any substance into another one; e.g., absolute nonexistence of cetana (sentience) in acetana (non- sentience) and the vice versa.
kālatrayāpekṣiṇī hi tādātmyapariṇāmanivṛttiratyantābhāvaḥ.yathā - cetanācetanayoḥ.
(Pranata 3.65,66)