Not surprisingly, the US Supreme Court’s non-decision on equal marriage has caused plenty of debate, including John H’s smackdown of NR’s Matthew Franck.

The discussion got me thinking about the broader problem of legal reasoning, at least in its originalist and textualist forms, and also in precedent-based applications of common law. The assumption in all of these approaches is that by examining (according to some system of rules) what was legislated or decided in the past, lawyers and judges can determine the law as it applies to the case at hand. There are all sorts of well-known difficulties here, such as how words written a century ago should apply to technologies and social structures that did not exist at the time. And it often happens that these approaches produce results that seem unacceptable to most people but for which a legislative or constitutional fix is impossible for some reason.

It’s always seemed to me, though, that there is a much bigger problem with this approach, namely the implicit assumption that “the law” actually exists. That is, it is assumed that, if the appropriate procedure is used to interpret the inherited text, and applied to the problem at hand, it will produce a determinate answer. But why should this be true? The same law might contain contradictory clauses, supported by contradictory arguments, voted in by different majorities, and understood at the time of its passage in contradictory ways. Most notably, the same constitution might grant universal freedoms in one place, while recognising slavery in another.

At a minimum, such contradictions mean that there is no determinate law on the particular points of difference. But the problem is worse than this. The law rarely prescribes an exact answer in a specific case. The standard view of legal reasoning is the principles can be extracted from case law, then applied to new cases. But contradictory laws and contradictory cases produce contradictory principles. The ultimate stopping point is the paradox of entailment: a contradiction implies anything and everything.

I don’t have a fully worked out answer to this problem but I think it underlies a lot of the disquiet so many people feel about legal reasoning (apart from the ordinary disappointment when the answer it produces isn’t the one we want).