In this paper I give a thorough account of the history of the open question argument. I have provide Moore’s original impetus for it and its traditional formulation. I then examine the Cornell Realists’ objection to that original formulation and showed that their objection does indeed show the open question argument to be incorrect in its conclusions. Having presented the history of the open question argument and having assessed the most challenging objections to it, I turn to Andrew Altman’s powerful reconstruction of the open question argument in order to see how well, if at all, it sidesteps the objections leveled against the classical formulation. I then argue that while Altman does present the most coherent defense of the open question argument available, I conclude that insofar as he has rested upon a commitment to Carnap's philosophy of language over a Fregean semantic and an untenable rendering of post-Kripkean philosophy of language as it concerns rigid designation, we must reject his reformulation. Given that rigid designation itself undermines Altman’s position, I conclude that the open question is still in need of a defense before it can regain its position as a major player in the discipline of ethics.

In this thesis, the main focus is on deontic logic as a tool for formal representation of moral reasoning in natural language. The simple standard system of deontic logic (SDL), i.e. the minimal Kripkean modal logic extended with the deontic axiom, stating that necessity (interpreted as obligation) implies possibility (interpreted as permission), has often been considered inadequate for this aim, due to different problems, e.g. the so-called deontic paradoxes. A general survey of deontic logic and the problems with SDL is made in chapter 1. In chapter 2, a system denoted Classical Deontic-Modal logic (CDM1) is defined. In this system, there is a primary obligation operator indexed to sets of possible worlds, and a secondary requirement operator, defined in terms of strictly necessary conditions for fulfilling an obligation. This secondary operator has most of the properties of the necessity operator in SDL. In chapters 3 and 4, it is argued that CDM1 is able to handle the SDL problems presented in chapter 1 in an adequate way, and the treatment of these problems in CDM1 is also compared with their treatment in some other well-known deontic systems. In chapter 5, it is argued that even though the problems related to quantification in modal contexts are relevant to deontic logic, these issues are not specific to deontic logic. In chapter 6, the relations between some controversial features of moral reasoning, such as moral dilemmas and “non-standard” deontic categories like supererogation, and deontic logic are discussed. It is shown how CDM1 can be modified in order to accommodate these features.