<p>This thesis is mainly a critical examination of Professor Mark C. Murphy’s theory of defectiveness. In his view, being backed by decisive reasons for action is a standard internal to legality, to the property of being law, such that a law or a legal system that is not backed by decisive reasons for action fails to measure up and thus, is <em>defective</em> qua law or legal system. Following a short introduction, I will devote chapter I to presenting Professor Murphy’s theory of defectiveness in the context of his defence of the natural law tradition. In the remaining two chapters, I shall state and assess two types of argument in support of this main thesis. Chapter II is concerned with the functional argument, which holds that law’s characteristic activity, thus law’s function, is to provide dictates backed by decisive reasons for action. I criticize Murphy’s account claiming that his explanation is bereft of a causal mechanism that links certain characteristic activities with certain effects, which is the main element of non-agentive functional explanations. The different type of argument that attempts to present the presence of decisive reasons as a non-defectiveness condition of illocutionary acts in general, and thus for legal illocutionary acts, is considered in chapter III. Here, I argue that Murphy’s position is not supported by the orthodox theory of illocutionary acts. From this I conclude that we have reason to doubt Professor Murphy’s success in providing an appropriate theory of legal defectiveness.</p> / Master of Arts (MA)