Developing Legal Arguments
The process of developing a legal argument is made in the "context of weighing and balancing legal principles" and the reasons and rationale behind the rules.
Weighing in the Law
The key topic in this context must be weighing and balancing. For legal both legal rules and juristic opinions are almost always justifiable with a recourse to weighing of various reasons. The reasons to be weighed are mostly values and principles. But I think that any rule can be weighed (cf. Peczenik 1989, 80 ff. and Verheij 1996, 48 ff.) against other reasons.
For example, statutory interpretation is an important field of legal argumentation where weighing of reasons, including moral ones, is inevitable. Various reasons and methods, such as literal interpretation, analogy, systemic interpretation, historical interpretation and goal interpretation support statutory interpretation in hard cases. The choice between the alternatives depends on weighing and balancing of various legal arguments (Peczenik 1995, 376).
What is weighed is prima facie. A prima facie rule thus do not determine definitive duties; the latter must result from weighing and balancing of all morally and legally relevant values, principles and rules in the particular case (cf. Peczenik 1995, 444 ff. and 484 ff.).
Legal reasoning is a form of theory construction. A judge rendering a decision in a case is constructing a theory of that case. It follows, then, that a lawyers job (in an appellate argument) is to construct a theory of the case, too, and one that just happens to coincide with his clients interest. Since the opposing lawyer is also constructing a theory of the case, which coincides with her clients interest, the argument boils down to this: Which theory should the judge accept? There are several constraints here, but they are weak ones. Legal theories should be consistent with past cases, and they should give acceptable results on future cases. They should not be too hard to understand, or too hard to administer, which means that they should be free of major anomalies. One term that is sometimes used to describe these requirements is coherence. Although difficult to specify precisely, the link between coherent legal theories and persuasive legal arguments seems to be strong.