  In this paper we prove an $\infty$-categorical version of the reflection
theorem of Ad\'amek-Rosick\'y. Namely, that a full subcategory of a presentable
$\infty$-category which is closed under limits and $\kappa$-filtered colimits
is a presentable $\infty$-category. We then use this theorem in order to
classify subcategories of a symmetric monoidal $\infty$-category which are
equivalent to a category of modules over an idempotent algebra.
