 One definition given by Boulding for knowledge was "the subjective 'perception of the world and one's place in it'", while Zeleny's said that knowledge "should refer to an observer's distinction of 'objects' (wholes, unities)".Zins, likewise, found that knowledge is described in propositional terms, as justifiable beliefs (subjective domain, akin to tacit knowledge), and sometimes also as signs that represent such beliefs (universal/collective domain, akin to explicit knowledge).Zeleny has rejected the idea of explicit knowledge (as in Zins' universal knowledge), arguing that once made symbolic, knowledge becomes information.