Theories of global justice are often criticised for being ineffective or unrealisable. The aim of this interdisciplinary thesis is to examine whether this motivational criticism holds regarding Singer’s Principle and Pogge’s theory of global egalitarian justice. First, I will show that the effectiveness argument is unconvincing: the underlying effectiveness criterion is either incoherent or not defined, and existing effectiveness predictions are empirically unsatisfactory. Second, I will analyse whether Singer’s interactional Principle satisfies the ‘ought implies can’ (OIC) criterion, which holds that obligations must be within the capacities of individuals. Having discussed the rationale and standard of the OIC criterion, I will show that the philosophical literature does not offer a convincing empirical justification of possibility evaluations. Drawing on psychological explanations of moral heroism, I will conclude that compliance with Singer’s Principle is possible for ordinary persons, i.e. that ‘every person is a hero in waiting’. Third, turning to the feasibility of Pogge’s theory of global egalitarian justice, I will discuss how the standard, time-frame, weight and rationale of the feasibility criterion should be defined. Based on psychological and sociological explanations about moral behaviour, social norms and identity, I will evaluate the empirical arguments advanced in the philosophical literature. In addition, I will consider how the long-term trends of globalisation are likely to influence the role of nationality, identity and global institutions. I will conclude that Pogge’s theory of egalitarian global justice is conditionally feasible, i.e. if we assume that domestic egalitarian justice is feasible. This implies that nationalism will not necessarily play a dominant role during the centuries to come. Overall, possibility and feasibility evaluations remain uncertain and partly subjective. I will thus argue that a burden of proof should be established to limit the negative effects of false evaluations.