Drawing general inferences on the basis of single-case and small-n studies is often seen as problematic. This article suggests a logic of generalization based on thinly rationalistic social mechanisms. Ideal-type mechanisms can be derived from empirical observations in one case and, based on the assumption of thin rationality, used as a generalizing bridge to other contexts with similar actor constellations. Thus, the "portability" builds on expectations about similar mechanisms operating in similar contexts. We present the general logic behind such "rationalistic generalization" and relate it to other ideas about generalization from single-case studies.