- a knowledge of what good and evil are,
- a desire and talent to choose good over evil,
- sufficient will power to execute that choice.
When a person sins he chooses evil over good, indicating that at least one of these gifts is missing.
Sin is therefore an indication that god has failed to dispense these gifts in sufficient abundance (or refrained from dispensing them by choice). Humanity is not to blame for the existence of sin, god is.

