nLab
full subcategory

Contents

Definition

If one accepts the notion of subcategory without any qualification (as discussed there), then:

A subcategory S of a category C is a full subcategory if its inclusion functor is a full functor.

This inclusion functor is often called a full embedding or a full inclusion.

Notice that to specify a full subcategory S of C, it is enough to say which objects belong to S. Then S must consist of all morphisms whose source and target belong to S (and no others). One speaks of the full subcategory on a given set of objects.

This means that equivalently we can say:

A functor F:SC exhibits S as a full subcategory of C precisely if it is a full and faithful functor. (S is the essential image of F).