托马斯·阿奎那认为,允诺就是允诺人为自己设定的法律,守约是一个人在自然法下的道德义务。道德行为的目的决定行为的实质或定义,并进而决定此行为的义务范围。而道德行为的最终目的是当事人试图践行的两种德性:慷慨的德性或交换正义的德性。托马斯·阿奎那实现了对亚里士多德哲学的承继和超越,二者共同为民法法系“原因理论”提供哲理基础,并弥补了近现代及当代合同法理论在对合同效力解释力上的不足。 Thomas Aquinas argues that promises are laws that promise people to set themselves, and that compliance is the moral obligation of a person under natural law. The purpose of moral conduct determines the substance or definition of the act and, in turn, determines the extent of the obligation to do so. The ultimate goal of moral behavior is that the parties try to practice the two virtues: generous virtue or the exchange of righteous virtue. Thomas Aquinas inherited and surpassed Aristotle’s philosophy. Both of them provide the philosophical basis for the Civil Law Law “cause theory ” and make up for the effect of modern and contemporary law of contract law on the contract Explanatory power deficiencies.