This paper probes the effects upon people of defining knowledge primarily in economic terms. It asserts that the language of commerce increasingly appropriates 'knowledge' by defining it in such terms. Theoretically, the analysis draws on the work of Jacques Derrida to explore the effects of metaphors in human resource management and development environments. The paper explores the ways that metaphors can become powerful signifiers of knowledge at work. As critical technologies of representation, the metaphors that have emerged out of recent theorizations of knowledge at work have contributed to a powerful discourse that defines people as 'knowledge workers'. It is argued here that dominant views of 'what constitutes a knowledge worker' imply that subjects are both 'knowledge workers' (cogito) and 'human resources' (economic) - thus the title 'cogito-economic subjects'. By defining people in this way, it is argued that there are potential dangers of metaphors becoming reified with knowledge becoming describable only in economic terms, and people describable only in cogito-economic terms.