Thornton, S. (2011) ‘Karl Popper’, in E.N. Zalta (ed.), The Stanford Enclyclopedia of Philosophy (Winter 2011 edition) http://plato.stanford.edu/archives/win2011/entries/popper/
Wettersten, J.R. (2007) ‘Karl Popper: Critical Rationalism’, in J. Fieser and B. Dowden (eds) Internet Encyclopedia of Philosophy. http://www.iep.utm.edu/cr-ratio/