When discussing any question in which a human being has a moral claim or a moral choice to make we need to address the justification of those claims and actions. Hence one can ask the question whether we can discuss a justification of moral judgments without having any specific knowledge about any corresponding fact or if it is possible to justify a moral judgment without having that kind of knowledge. This thesis has critically assessed Rainer Forst’s justification theory in relation to moral epistemology, aiming at clarifying his position on the matter. The study shows that Forst’s position is one of a cognitivist nature with a form of rational constructivism. The thesis suggests an alternative approach to Forst’s justification theory. Forst should take on an empiricist explanation when it comes to justifying moral judgements and therefore an epistemology that is not rationalism. Therefore, I suggest a form of realism when it comes to the discussion of his ontology.