Explain the four concepts necessary for a mature understanding of death.

Nonfunctionality, the understanding that death entails the complete and final end of all life-defining abilities or functional capacities, internal and external, that are typically attributed to a living body.
Irreversibility, the understanding that the processes involved in the transition from being alive to being dead and the resulting state of being dead cannot be undone. Once a thing dies, its physical body cannot be made alive again.
Inevitability, the understanding that death is universal, that all living things will someday die.
Biological causality, the understanding that death is caused by events or conditions that trigger natural processes within the organism and that it is not caused by bad behavior or wishes.