康德在《道德形而上学奠基》中提出第二条定言命令，即“始终把人格中的人性当做目的而不仅仅当做手段”的道德诫命是成为现代社会最常被援引的道德格言之一。但是，这条命令中的核心概念“人性”应当作何理解却是一个充满争议的问题。在以《道德形而上学奠基》为代表的的道德哲学著作中，康德并未对这一概念做出充分的解释，这也给继续解读留下了空间。其中留存了以下几个重要问题亟待回答：第一，康德是如何将“目的自身”概念与“人性”概念等同起来的；第二，以“人性”作为“目的”的准则，是如何成为一种客观法则的；第三，“人性”概念是什么。哈佛大学教授Christine Korsgaard在上世纪80、90年代发表的一系列论文中提出了后来被称为“回溯性论证”的解读手法，通过对《道德形而上学奠基》文本的重新解读认定，康德所说的必须被当做目的自身的“人性”，指的是人设定目的，即为对象赋予价值的能力。她将康德文本中对偏好的对象、偏好自身、非理性存在物的否定论证视为一种回溯过程，回溯的终点，就是那个不能被继续当做目的的目的自身，即人为自身设定目的的能力。Richard Dean从另一个角度回应康德的问题，他不像Korsgaard从文本出发，而是反过来从“人性”概念与道德法则的应用角度出发，认为，传统意义上的“人性”理解过于保守，总是以“为绝大多数人赋予道德资格”为目标，这才造成了解读上的种种矛盾之处。他旗帜鲜明地提出，应当将“善良意志”视为给道德法则奠定基础的“目的自身”，也就是“人性。”他重新解释了“善良意志”概念，将它解读为一种可以被长久拥有的属性，而非是一种瞬时的状态，而后将这一概念应用于“人性公式”中。将“人性”概念理解为人的自主性是一个由来已久的康德诠释传统，近年来，这种进路中最富创新性的成果是Oliver Sensen的观点。Sensen首先颠覆了对“目的自身”概念的传统理解，认为这个概念本身不包含规范性，而只是一种描述性概念，并通过对康德多种文本的大量研究指出，这一概念描述的对象就是“自由”概念。按照这种解读，“人性公式”法则并非如许多哲学家怀疑的那样，是一条独立的定言命令，而只能建立于“可普遍化原则”的基础之上，康德的定言命令形式也可以籍“自由意志”为媒介达成统一。
The colorful modern society has spawned a variety of different moral principles, and Kantian moral philosophy has always played a fundamental role of them. The second categorical imperatives has become the most commonly quoted moral slogan in modern society. By contrast, what should be understood as the core concept of ＂humanity＂ in this imperative is controversial. In his works, Kant did not fully explain this concept, leaving room for continued interpretation. There are several important issues that remain to be answered: First, how did Kant equate the concept of ＂end in itself＂ with the concept of ＂humanity＂? Second, how does the principle of “humanity should be treated as end and not merely as means” become an objective law. Third, what is the concept of “humanity”? Harvard professor Christine Korsgaard proposed an interpretation method that was later referred to as “regress argument” in the 1980s and 1990s. By reinterpreting the text “Groundwork of the Metaphysics of Morals”, Korsgaard holds that the concept of humanity refers to the ability of the person to set an end. Richard Dean responds to Kant‘s question from another side. He believes that the traditional understanding of ＂humanity＂ is too conservative. He clearly proposed that ＂good will＂ should be regarded as ＂end in itself＂ that lays the foundation for moral principles, that is, ＂humanity.＂ Understanding the concept of “humanity” as “autonomy” is a long-established tradition of Kant interpretation. In recent years, the most innovative result of this approach is Oliver Sensen‘s point of view. Sensen first subverted the traditional understanding of the concept of ＂end in itself＂ by saying that the concept itself is not a normative but a descriptive concept, and pointed out this concept is a description of ＂freedom＂ through research on Kant‘s various texts. According to this interpretation, the “Formula of Humanity” is not an independent imperative, as many philosophers suspect, but can only be based on the principle of “Universal Law”. Kant’s forms of categorical imperatives are also united into one through the mediation of ＂free will＂.
