Max Horkheimer ( 1972), one of the founders of the Frankfurt School of critical theory (Jay, 1973; Wiggershaus, 1994), described critical theory as a form of theorizing motivated by a deep concern to overcome social injustice and to establish more just social conditions for all people. He contrasted critical theory with 'traditional theory', by which he meant posi­tivistic science, what in this volume is referred to as conventional science, which aims to build scientific knowledge progressively by accumulating empirical knowledge of the world, assuming a distinction between facts and values. Critical theory, Horkheimer said, < has no specific influence on its side, except concern for the abolition of social injustice .... Its own nature ... turns it towards a changing of history and the establishment of justice (Horkheimer, 1972: 242-43). > The notion of 'critique' in critical theory means exploring 'existing conditions' (Marx, 1967) to find how particular perspectives, social arrangements, or practices may have irrational, unsustainable, unjust, alienating, or inhumane consequences. The classical case is Marx's (1977) Capital (first published in German 1867, first English edition 1887), his analysis of class relationships under capi­talism that produced and reproduced the suf­fering of working-class people while at the same time producing and reproducing the advantages of ruling class people and groups. In critical participatory action research, participants aim to be 'critical' in this way, to find how particular perspectives, arrange­ments and practices create untoward effects. Through critical participatory action research, they aim to change things so untoward con­sequences can be avoided, acting negatively against real and manifest irrationality, unsus­tainability, and injustice, rather than posi­tively for some elusive ideal of what counts as rational, sustainable, or just.