It has been claimed that an action is morally good only if it benefits another person and was performed with that intention; whereas an action that harms another person is morally bad either if such harm was intended or if reasonable forethought would have shown that the action was likely to cause harm.
Principle
only if = right side, if = left side
Action morally → Benefits another person good and performed w/ that intent
Someone else harmed and → morally bad (Harm intended OR reasonable forethought would have shown action likely to cause harm)
Evaluate
We always want the "judgy", normative language on the right side of the rule. In this paragraph, the normative language is about whether actions are morally good or bad, so we need to contrapose the first rule.
Doesn't benefit someone else action not or → morally good Not performed w/ that intent
The 2nd rule is a little sneaky because it's not about any action. It's specifically have "an action that harms another person".
We could have added that concept to the trigger, if we prefer thinking about it that way:
.
Goal
We have rule 1 which has the power to prove something is "not morally good" (which doesn't mean the same thing as morally bad. Actions can be amoral, neither good nor bad).
We have rule 2 which has the power to prove that a harmful action is "morally bad".
We'll get rid of any answer that's trying to conclude something other than "not morally good" or "morally bad".
And based on the conclusion, we'll know whether to look at the trigger for rule 1 or rule 2.