So given: window.Post = Backbone.Model.extend({...}); window.Comments = Backbone.Collection.extend({...}); var p = new Post( id: 3, te

So given: window.Post = Backbone.Model.extend({...}); window.Comments = Backbone.Collection.extend({...}); var p = new Post( id: 3, text: 'test', comments: [ { cid:4, bleh:5}, {c id:6, bleh:4} ] }); You want some way to declare that comments are Comments, so that it is always the case that: (p.attributes.comments instanceof Comments) === true And you also want: p.attributes.comments.add({...}); To trigger a 'change:comments' event on p, even though you aren't changing the reference to the comments collection, just changing its comments. Do I understand you correctly?