J.S. Mill believed that the meanings of singular terms were their denotations. Denotations are usually seen as objects of some description. Therefore any proposition which had a term whose meaning was its denotation would literally(?) have an object within it.
In terms of the modes of presentation of an object, it can also be said that a criterion of identity must come along with a “principle of unity”. In addition, an object must have some kind of temporal longevity if it's to be deemed an object in the first place.