Contents

Definition

The term simplicial category has at least three common meanings. Thus, to avoid ambiguity, it is perhaps better to avoid it entirely and use an equivalent, unambiguous term for the particular meaning one has in mind.

• The simplicial category $\Delta$ is the domain category for the presheaf category of simplicial sets. This is the full subcategory of Cat on categories which are linear quivers, or equivalently the category of finite, non-empty totally ordered sets and order-preserving functions between them. To avoid ambiguity, $\Delta$ may also be called the simplex category or the simplicial indexing category.

• A simplicial category is a simplicial object in Cat (that is, a functor from ${\Delta }^{\mathrm{op}}$ to $\mathrm{Cat}$), just like a simplicial set is a simplicial object in Set, a simplicial space is a simplicial object in Top, a simplicial abelian group is a simplicial object in Ab, and so on. To avoid ambiguity, simplicial objects in Cat may be called exactly that.

• A simplicial category also frequently means a category enriched over the category of simplicial sets, i.e. an sSet-enriched category. Such categories can be identified with simplicial objects in Cat all of whose face and degeneracy morphisms are bijective on objects. To avoid ambiguity, categories enriched over simplicial sets may be called simplicially enriched categories.

Related concepts

• simplicial category

  • simplicially enriched category

  • simplicial object in Cat

• simplicial groupoid

• relation between quasi-categories and simplicial categories