This thesis analyses a corpus of 936 instances of the structure “I + copula + NOT + indefinite noun phrase” and its variants, as used in UK web forums. Making assertions about one’s identity in the negative not only provides information about what one claims not to be, but also indexes various aspects of, and potentially modifies, the interpretation of the textual and non-textual context in which such assertions are used. The thesis develops a theoretical and methodological framework to qualitatively and quantitatively identify the multifunctional, context-dependent meaning potential of the structure in focus. The corpus was qualitatively analysed and tagged for conceptual categories of identifying NPs as well as for formal and functional features of the co-texts in which the structure appears. A conceptual profile of negative self-identifiers was developed, and the experiential meanings of the immediate context of the structure were examined, as were their relations of co-occurrence with particular conceptual categories of negative identifiers. By investigating whether users of English in particular co-texts negate self-identification with noun phrases from particular conceptual domains in patterned ways, the study identified certain conceptualisations that were implicitly acknowledged as relevant for people’s self-representation in these discourse contexts. Key findings include: (a) negative identification with expertise is a frequent linguistic choice in the context of presenting one’s knowledge; and (b) negative identification with preferences is a frequent linguistic choice in contexts describing one’s experience. These findings are discussed in light of the wider sociopolitical context, suggesting an ideological struggle around – and a possible reconceptualisation of – the notion of epistemic authority.