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

诉诸法律错误是否可以防止法律上的弊端，这是一个经典的法理学问题。罗马法律中的短语“Error iuris nocet”--法律的错误是有害的--广为人知。这个问题通常是从刑法的角度来研究的，但这个问题在私法中也具有根本性的重要性。需要澄清“法律错误”的概念。这里介绍的工作表明，这一术语选择不当，因为它不一定包括(故意的)法律不确定性的情况。然而，正是在这一领域，至少在最近的过去，实际的实际相关性已经变得明显。德国私法在不同的背景下对待法律错误和法律不确定性的方式非常不同。范围从宽松到极度严格不等。这些差异激怒了许多观察人士。顺应性论题表明，流行的方法并不像乍看上去那样在结果上相互矛盾。为了证明这一点，该论题为法律错误领域发展了一个新的理论框架。它被分成四个“象限”。在第一个层面上，区分了认为自己是正确的假设和低估了自己的权利。在第二个层面上，可以区分对索赔的追索和抗辩。错误地未能追查现有索赔和错误地抗辩第三方索赔往往会给犯错方(处方、赔偿责任)带来相当大的不利影响。另一方面，在错误地追求索赔或未能针对不存在的索赔为自己辩护时，法律错误往往会阻止不利的情况。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。这些首先可以在民事诉讼法中找到--这一领域迄今在法律错误的背景下基本上被忽视了。特别是，澄清悬而未决的法律问题具有普遍的利益。在这方面，在法律不确定的情况下提供足够的激励是至关重要的。在这一学理分析之后，本文制定了具体的标准，以便于实际处理法律错误。总而言之，这表明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同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.