A note on the categorical van Kampen Theorem

In this note we show that for the canonical map X₁+X₂→X, from the topological sum of two subspaces X₁, X₂ of X into X, to be of effective descent it is sufficient to be hereditarily a quotient map. Further, making use of the Brown-Janelidze categorical van Kampen Theorem, this translates into a van Kampen-type result.