In Ethics in the First Person, Deni Elliott defines permissibility thusly:
A moral system differentiates among behaviors that are morally prohibited, those that are morally permitted, those that are morally required, and those that are morally encouraged.... Permitted [means] behavior that is within the bounds of the moral system. It is morally permitted to act in any way that does not cause others unjustified harms.In short, "permitted" is the lowest bar for moral behavior. Anything that is not morally forbidden is permitted.
Another way to look at it: we tolerate permissible behavior, even if we disagree with it or find it distasteful. Jovan Babic, in "Justifying Forgiveness," found in Peace Review, March 2000, explains:
Tolerance is the demarcation line between that which is permissible and that which is impermissible. In practice, what is morally permissible is what is in a way morally indifferent, and it is the subject of legitimate freedom, while what is morally impermissible can absolutely not be tolerated and its tolerance (by others) would mean abandoning the basic principle of moral evaluation (in oneself)."Legitimate freedom," to Babic, means a choice between actions without any sort of moral stricture--either proscription, encouragement, or obligation.
Context can be crucial in determining whether a moral choice is permissible. Consider Carla, who wishes to play a board game.
1. Choosing to play Monopoly instead of Risk is (probably) morally insignificant; either choice is morally permissible.
2. Choosing to play Monopoly instead of finishing her chores and homework could be morally prohibited.
3. Choosing to play Monopoly in a marathon to raise money for cancer research could be morally encouraged.
4. Choosing to play Monopoly according to the rules could be morally required.
The crucial thing to note regarding the current resolution is that the affirmative, in showing that trading one life for many is morally permissible, does not have to prove such an action is right, but only that it isn't wrong.
I'm still searching for other good definitions of "morally permissible." If you find one, let me know.