Mistake of law and legal uncertainty regarding the pursuit of and the defence against claims

诉诸法律错误是否能防止法律的不利是一个经典的法理学问题。罗马的法律的短语“error iuris apriet”--法律的错误是有害的--广为人知。这一问题往往从刑法的角度加以审查，但这一问题在私法中也具有根本重要性。“法律错误”的概念需要明确。本文介绍的工作表明，这一术语选择不当，因为它不一定涵盖（故意的）法律的不确定性的情况。然而，正是在这一领域，至少在最近的过去，实际的现实意义变得明显，德国私法在不同的背景下对待法律错误和法律的不确定性有很大的不同。范围从宽到严。这些差异激怒了许多观察家。这篇论文表明，主流的研究方法并不像乍看上去那么自相矛盾，为了证明这一点，本文为法律错误领域建立了一个新的理论框架。这分为四个“象限”。在第一个层次上，区分了假设自己是正确的和低估自己的权利。在第二个层次上，可以区分提出索赔和对索赔进行抗辩。错误地不提出现有的索赔要求和错误地对第三方索赔要求进行抗辩，通常会给犯错误的一方带来相当大的不利影响（时效、赔偿责任）。另一方面，当涉及到错误地追求要求或未能对不存在的要求进行辩护时，法律错误往往会防止不利的情况发生，正如所证明的那样，这些不同的结果在很大程度上可以用统一的方面来解释。这些可以首先在民事诉讼法中找到-这是一个迄今为止在法律错误方面基本上被忽视的领域。特别是，人们普遍希望澄清尚未解决的法律的问题。在这方面，在法律的不确定性的情况下，提供足够的激励是至关重要的。总之，目前的系统仍然可以在许多方面进行优化-尤其是考虑到智能合约和人工智能的未来意义。

Whether recourse to a mistake of law can protect against legal disadvantages is a classic question of jurisprudence. The Roman legal phrase "error iuris nocet" – the mistake of law is harmful – is widely known. The problem is often examined in the light of criminal law, but the issue is also of fundamental importance in private law. The concept of “mistake of law” needs to be clarified. The work presented here demonstrates that the term is poorly chosen as it does not necessarily cover cases of (deliberate) legal uncertainty. However, it is precisely in this area that, at least in the recent past, the actual practical relevance has become apparent.German private law treats mistakes of law and legal uncertainty very differently in different contexts. The spectrum ranges from leniency to great strictness. These discrepancies irritate many observers. The habilitation thesis shows that the prevailing approach is by no means as contradictory in its results as it may seem at first glance.To prove this, the thesis develops a new doctrinal framework for the field of mistakes of law. This is divided into four "quadrants". On a first level, a distinction is made between the assumption of being in the right oneself and an underestimation of one's own rights. On the second level, a distinction can be drawn between the pursuit of and the defence against claims. The erroneous failure to pursue an existing claim and the erroneous defence against third-party claims regularly lead to considerable disadvantages for the erring party (prescription, liability). On the other hand, mistakes of law oftentimes prevent disadvantages when it comes to the erroneous pursuit of aclaim or the failure to defend oneself against non-existing claims.As is demonstrated, these different results can be explained, to a great extent, by uniform aspects. These can be found above all in the law of civil procedure – a field that has so far been largely neglected in the context of mistakes of law. In particular, there is a general interest in the clarification of unresolved legal questions. In this respect, it is crucial to provide sufficient incentives in cases of legal uncertainty.Following this doctrinal analysis, the thesis develops concrete standards to facilitate the practical handling of mistakes of law. In conclusion, it is shown that the current system can still be optimised in many respects – not least in view of the future significance of smart contracts and artificial intelligence.