Some well-known legal philosophers use both pairs of terms -- "principle" vs. "policy" and "rights" vs. "goals" -- to mark what they see as two classes of considerations for legal decisionmaking that they find it important to distinguish for certain purposes. Learning the arts of legal reasoning and argument does not require mastering terminological niceties of philosophical usage (and in fact my use of the term "policy argument" in what follows is quite deliberately contrived to cut across the principle/policy and rights/goals distinctions. However, the philosophers' distinctions do quite nicely track practicing lawyers' own intuitions about different "kinds" of legal policy arguments that may be available, and for that reason it's definitely worthwhile for you to get to know what the "principles"/"policies" and "rights"/"goals" distinctions are driving at. See Ronald Dworkin, Taking Rights Seriously (Cambridge, Massachusetts; Harvard University Press, 1977), pp. 82-83, 169-71.