model structure on sSet-categories


Model category theory

model category



Universal constructions


Producing new model structures

Presentation of (,1)(\infty,1)-categories

Model structures

for \infty-groupoids

for ∞-groupoids

for nn-groupoids

for \infty-groups

for \infty-algebras



for stable/spectrum objects

for (,1)(\infty,1)-categories

for stable (,1)(\infty,1)-categories

for (,1)(\infty,1)-operads

for (n,r)(n,r)-categories

for (,1)(\infty,1)-sheaves / \infty-stacks

(,1)(\infty,1)-Category theory



Depending on the chosen model category structure, the category sSet of simplicial sets may model ∞-groupoids (for the standard model structure on simplicial sets) or (∞,1)-categories in the form of quasi-categories (for the Joyal model structure) on SSet.

Accordingly, there are model category structures on sSet-categories that similarly model (n,r)-categories with rr shifted up by 1:

This we discuss below.

Both are special cases of a model structure on enriched categories.

Model for (,1)(\infty,1)-categories

Here we describe the model category structure on SSet Cat that makes it a model for the (∞,1)-category of (∞,1)-categories.


An sSet-enriched functor F:CDF : C \to D between sSet-categories is called a weak equivalence precisely if

Such a morphism is also called a Dwyer-Kan weak equivalence after the work by Dwyer-Kan on simplicial localization.


A Quillen equivalence CDC \stackrel{\leftarrow}{\to} D between model categories induces a Dwyer-Kan-equivalence LCLDL C \leftrightarrow L D between their simplicial localizations.


The category SSet Cat of small simplicially enriched categories carries the structure of a model category with

(Bergner 04)


In particular, the fibrant objects in this structure are the Kan complex-enriched categories, i.e. the strictly ∞-groupoid-enriched ones (see (n,r)-category).



The Bergner model structure of prop. 2 is a right proper model category.

(Bergner 04, prop. 3.5)

The entries of the following table display models, model categories, and Quillen equivalences between these that present the (∞,1)-category of (∞,1)-categories (second table), of (∞,1)-operads (third table) and of 𝒪\mathcal{O}-monoidal (∞,1)-categories (fourth table).

general pattern
strict enrichment(∞,1)-category/(∞,1)-operad
enriched (∞,1)-category\hookrightarrowinternal (∞,1)-category
SimplicialCategories-homotopy coherent nerve\toSimplicialSets/quasi-categoriesRelativeSimplicialSets
\downarrowsimplicial nerve\downarrow
SimplicialOperads-homotopy coherent dendroidal nerve\toDendroidalSetsRelativeDendroidalSets
\downarrowdendroidal nerve\downarrow


A model category structure on the category of sSetsSet-categories with a fixed set of objects was first given in

  • William Dwyer, Dan Kan, Simplicial localization of categories , J. Pure and Applied Algebra 17 (3) (1980),

Dywer, Spalinski and later Rezk then pointed out that there ought to exist a model category structure on the collection of all sSetsSet-categories that models the (∞,1)-category of (∞,1)-categories. This was then constructed in

A survey is in section 3 of

See also section A.3.2 of


Recall the slight but crucial difference between the two notions of “simplicial categories”, the other being an internal category in sSet. But also for this latter concept there is a model category structure which presents (infinity,1)-categories, see

  • Geoffroy Horel, A model structure on internal categories, Theory and Applications of Categories, Vol. 30, 2015, No. 20, pp 704-750 (arXiv:1403.6873).

Last revised on May 27, 2015 at 04:00:47. See the history of this page for a list of all contributions to it.