Critics often argue that Ross’s metaphysical and epistemological accounts of all-things-considered duties suffer from the problem of explanation. For Ross did not give us any clear explanation of the combination of pro tanto duties, i.e. how principles of pro tanto duties can combine. Following from this, he did not explain how we could arrive at overall justified moral judgements. In this paper, I will argue that the problem of explanation is not compelling. First of all, it is based on the classical account of pro tanto duties. Principles of pro tanto duties can be understood in another way, i.e. in terms of reason-giving account that might be of help to provide a response to the critics. Furthermore, critics fail to see some evidence in Ross about how we can arrive at moral judgements.

Key words: W. D. Ross, pro tanto duty, all-things-considered duty, the problem of explanation, reason-giving account.