Resolving conflicts between different laws can be handled by the reciprocity principle. Reciprocity means that a party is judged by the same law by which that party would judge others. Therefore, in the context of voluntary law, this means that the defendant’s choice of law has priority, in the event of a conflict of laws.
Defendant’s “choice” cannot be based on an opportunistic selection made with a particular claim in mind. Instead, the choice is determined by which law or laws the defendant has adopted at any time since just before the earliest event giving rise to the claim, or since some other earlier time. If the defendant has adopted different laws during the applicable period, the applicable law can be the one that would result in the greatest liability for the defendant. This rule of “defendant’s law of greatest liability” disincentivizes opportunistic adoption of lenient laws to escape liability for planned evil deeds.
The reciprocity principle and greatest liability rules work at least reasonably well for claims based on personal harms such as murder, battery, rape, kidnapping, etc., for the simple reason that every person has a body and therefore faces the same or similar risks of suffering personal harms.
One can hypothesize that the reciprocity principle would not work well for relations between mortal and immortal persons, because of the imbalance of risks. For example, an immortal person might prefer a law that permits murder freely without penalty, because the immortal person cannot be murdered. The immortal therefore might prefer that there be no penalty for murder to reduce the risk of facing claims of murder from others, without in any way increasing her own risk of being murdered or need to recover damages for her own untimely death. This problem might be called the “impossibility problem” because it is impossible for a class of persons to suffer the same harms as another class of persons, so reciprocity becomes impossible.
While the existence of immortal persons is merely hypothetical, the impossibility problem is a present reality for claims based solely in property rights, for the simple reason that not everybody holds the same types of property. While virtually everybody has personal property of some kind, some may own no real property (e.g., land), or no “intellectual property.” Consider, for example, the case of copyright. Creators of books and so forth might generally prefer the ability to make claims against those who copy their works without permission. Mere consumers of books, on the other hand, might generally favor no such penalties. Under the principle of reciprocity, there is no way for a content creator to bring a copyright claim against a mere consumer who has not adopted any law recognizing copyrights as a class of property or claims. Whether you consider that outcome good or bad, it provides an example of the impossibility problem at work.
One can imagine similar problems in real property. For example, suppose one person (Lysander) adopts a law that adverse possession requires open and unchallenged use for a continuous period of three years. Another person (Murray) adopts a law requiring only one year of open and unchallenged use. Murray openly squats unchallenged on Lysander’s land for 2 years, at which time Lysander sues to evict Murray. Murray countersues to claim Lysander’s title. Applying defendant’s rule to Lysander’s claim, Murray wins. Applying defendant’s rule to Murray’s claim, Lysander wins. Therefore, Lysander cannot legally evict Murray, nor can Murray obtain Lysander’s title. The practical result may be that Murray can stay rent-free for as long as he pleases, but will never be able to obtain legal title because Lysander challenged Murray’s presence within three years.
The foregoing examples illustrate how the reciprocity principle might create social pressure for property laws of minimal reach. In other words, practically enforceable property claims in a universe of voluntary law societies might tend to be those that are universally accepted as being valid. Simple claims result in application defendant’s rule only, while in the case of counterclaims mixed results such as in the adverse possession example are achieved. This is an interesting result, and not necessarily a bad thing; it may even be a marvelous, beneficial feature of voluntary law.
It is not easy to conceive of conflict of law rules based on a principle other than reciprocity, without destroying even more fundamental precepts of voluntary law such as the prohibition on imposing laws involuntarily. It may be that a tendency to diminish property claims towards a universally accepted minimal common denominator is a logically necessary aspect of voluntary law. Or, perhaps the impossibility problem can be solved for property claims without involuntarily imposing the claimant’s law on defendants. Either way, the impossibility problem in resolving conflict of laws is interesting to think about.