The current view of theoretical statements in science is that they should be literal and precise; ambiguous and metaphorical statements are useful only as pre-theoretical, exegetical, and heuristic devices and as pedagogical tools. In this paper we argue that this view is mistaken. Literal, precise statements apply to those experiential phenomena which can be defined either conventionally by criterial attribution or by internal atomic constitution. Experiential phenomena which are defined relationally and/or functionally, like nursing, in virtue of their nature, require metaphorical description and explanation. In such cases, metaphor is theory-constitutive. Using insights from the philosophies of language and mind, and examples from nursing practice, education, and our own empirical research, we explore the nature of metaphor and its role in theory constitution. We argue that the apparent resistance of certain experiential phenomena to literal description and explanation is not necessarily indicative of pre-theoretic linguistic imprecision. We suggest, rather, that such resistance provides useful insights into the nature of such experiential phenomena. We also suggest that the aim of scientific theory should be methodological or epistemological precision and not merely linguistic precision.