Section 36 of the Swedish Contracts Act stipulates that a term of a contract can be modified or set aside, if it is "unreasonable". The thesis discusses the meaning of the prerequisite "unreasonable" and how the meaning can and should be defined, using the means of legal science. Normative ethics is thereby introduced as a supplementary source of norms, and scientific works regarding contract law in other European countries are regarded, as well as the Principles of European Contract Law.
One chapter deals primarily with legal theory, in particular how a position regarding a legal matter can be justified. The role of normative ethics, especially virtue ethics, in legal science is discussed in that context and "the virtues of the contractual relationship" are identified (for example justness, honesty, carefulness). The following chapter focuses on the relationship between those virtues and some principles of contract law (for example the principle of trust, the principle of loyalty), and it is being maintained that the value basis for the virtues on the one hand and the principles on the other hand is largely the same. It is also being maintained that there are strong arguments in favour of letting the virtues and principles affect the definition of the prerequisite "unreasonable" in section 36.
In the last major chapter, four cases are used as starting points of a discussion regarding various situations, in which "unreasonable" has to be defined. The impact on the definition of "unreasonable" of the previously introduced virtues and principles is discussed, as well as the significance of various circumstances. The duty of disclosure, the significance of balance between the rights and duties of the parties under the contract and the importance of events occurring after the conclusion of the contract are some of the issues, which are treated.