  Any modality in homotopy type theory gives rise to an orthogonal
factorization system of which the left class is stable under pullbacks. We show
that there is a second orthogonal factorization system associated to any
modality, of which the left class is the class of $\bigcirc$-equivalences and
the right class is the class of $\bigcirc$-\'etale maps. This factorization
system is called the reflective factorization system of a modality, and we give
a precise characterization of the orthogonal factorization systems that arise
as the reflective factorization system of a modality. In the special case of
the $n$-truncation the reflective factorization system has a simple
description: we show that the $n$-\'etale maps are the maps that are right
orthogonal to the map $\mathbf{1} \to \mathbf{S}^{n+1}$. We use the
$\bigcirc$-\'etale maps to prove a modal descent theorem: a map with modal
fibers into $\bigcirc X$ is the same thing as a $\bigcirc$-\'etale map into a
type $X$. We conclude with an application to real-cohesive homotopy type theory
and remarks how $\bigcirc$-\'etale maps relate to the formally etale maps from
algebraic geometry.
