Corpus linguistic techniques are increasingly being used by discourse analysts whose interest is in the ‘critical’ issues of inequality and the representation of disadvantaged groups. This paper reports an extension of these approaches, where concordancing was used to analyse a corpus of 144 transcribed oral history interviews in order to explore the issue of constraint on the speakers’ goals and experiences. The analysis is of the expression I couldn't, which is contextualised with reference to research on negation and modality in authentic discourse contexts. This paper explores the ways in which I couldn't is deployed to refer to constraints of three main kinds: physical (pertaining to the body and material objects), structural (pertaining to the distribution of resources) and cultural (pertaining to social norms and expectations). The approach illustrates the advantage of maintaining an analytical distinction between the discursive and the material, so as to explore the interplay between them.