Although the methodologies for describing many types of linguistic variation have been well developed, satisfactory theoretical links between data and explanation – especially links that include causal mechanisms – remain lacking. This article argues, somewhat paradoxically, that even though most choices reflect some societal pattern, speakers make linguistic choices as individuals. That is, choices ultimately lie with the individual and are rationally based. Rational Choice Models (e.g. Elster 1979, 1989, 1997) provide explanatory mechanisms for the ways actors in society select from alternative structures and available options. The Rational Choice approach taken here is enhanced by diverse theories of human action (e.g. Damasio 1996, Klein 1998, Lessig 1995). Analysis of codeswitching examples within a recasting of the Markedness Model (Myers-Scotton, e.g. 1993, 1998) suggests how a rationally based model offers better explanations for linguistic variation than do other approaches.