1. Positivism = Only observable phenomena can provide credible data and facts. Focus on causality, generalization, reduce everything to its simplest forms.
2. Realism = Credible data and facts are the result of observable phenomena. Focus on the context of explaining.
3. Interpretivism = Focus on subjective meanings and social phenomena.
4. Pragmatism = Either/both observable phenomena and subjective meanings are acceptable as sources of knowledge. The research question should drive the method.
Source: Saunders et al. (2009)