I recently read a book called The Enchantment of Reason by Pierre Schlag and I highly recommend it to anyone interested in legal theory.
His thesis is that the basis of legal authority is on unstable footing. The legal discipline has built it's foundation on the temple of reason. However, reason is not as stable is commonly accepted. In fact the authority of reason is incredibly unstable. At worst the authority of reason is based circular reasoning (i.e. reason supersedes other forms of belief because it is reasonable) and at best it is constantly reexamining and destabilizing its own underpinnings - again making it very unstable - and ill-suited to law which is supposed to be stable.
Therefore, "legal reasoning" is really just a mask that hides the naked exercise of power of individuals over other individuals - i.e. judges and legal practitioners over other people.
I think Schlag goes a long way in demystifying this enchantment (contamination) of reason in the legal discipline. He says law is merely word games. (Deadly serious word games in which people's lives lie in the balance.) The law is self-referential and never expresses or even touches reality. Legal artifacts - statutes, judicial rules, etc. - have no existence outside of representations in our mind. Therefore when legal theorists justify decisions based on "reason" what they really are talking about is nothing more than "community consensus" or "belief in the reasonableness" of said decision.
Furthermore, not only is law based on belief, but this belief system called "legal reasoning" is often quite unreasonable. AS when a judge says "the law dictates this..." or "the law requires this...". In both cases the law is treated as a willing subject that demands things from us. Sometimes it goes so far as to demand the creation of new law to fill out the penumbra of the legal landscape. The way legal practitioners treat the law is ridiculous. The law has no will - it's no more a willing subject than a banana is a willing subject. (At least a banana is organic.) Legal theorists treat law as a willing subject in order to be "textual" and stick to the law alone. This perspective is seductive because it makes the law into something divorced from the messiness of human will. It reduces law to a series of axioms from which conclusions can be derived from the text alone.
But again, this seduction is ridiculous, it is not law that has will but is in fact people who wrote the law who are the willing subject. Enter the originalists who treat the law as the will of certain people - congress people, executive rule-makers, and the most mystical of all "The Constitutional Framers".
However to treat law as the will of individuals is incredibly messy and subjective, making consistency and reasonableness (the keystone of legal authority) highly unlikely. There are 535 people in Congress, a majority of which it takes to pass a bill into law. To pretend to know exactly what every one of them intended when they signed a bill into law is ridiculous. Even if you did obtain this knowledge through an act of transubstantiation (or by channeling a founding father) to say that all the different wills involved (with often contradictory intentions) can be combined into a consistent legal rule is ridiculous.
Add to this that in a democratic system representatives that write our laws base their authority on the will of the people. There may be a congressional record to shed some light on what Congress people thought they were willing when they voted for legislation - but what about the people who voted for them? How can we know what they intended when they selected such-and-such representative?
The Constitution of the United States specifically sets forth that the US government is established by "We the people". The authority of all US law derives from this democratic principle: that it is "the will of the people" that gives law authority. The willing subject behind the law is therefore all the people of the United States of America. How can a judge or litigator, examining a recently passed law, claim to know the will of every then living person in the United States?
The answer is they cannot. It is impossible to know each of those people individually and then to amalgamate all those wills into some kind of coherent whole. They can at best guess, and those guesses are always highly subjective and based on belief.
This is where I've gotten to in my thinking on US jurisprudence since reading Schlag's book. Anybody want to defend legal reasoning from my Schlagian critique of legal reasoning?