Professional Linguistics is an emergent area of study within applied linguistics, using discourse analysis to assist people working in professional domains. This book examines tacit knowledge - that expertise that is considered to be lost when skilled practitioners leave an institution. Traditionally it has been argued that some aspects practical knowledge cannot be articulated. However, the premise of Polyani's theory of Tacit Knowing ("we know more than we can tell") does not account for latent patterns that linguists can uncover in spoken language. Understanding these discourse patterns provides a way to explore the assumptions people invoke, but do not make explicit in their work and working relationships. This book demonstrates an interview method grounded in systemic functional linguistics that probes the spoken discourse of IT professionals, through three field studies with actual corporations. It argues that 'we tell more than we know' and this 'telling more' resides in the taken-as-given patters of grammar and semantics, making meaning in ways which speakers themselves may not be attuned to.