I am wondering which cases govern inclusion of the preposition with nouns in the ablative. I can only think of one situation which recommends this: when the ablative form of the noun, in the absence of diacritical marks, is identical to another case form of the noun (for instance, abstract nouns in -ia, where the ablative -iā is identical to the nominative -ia if the macron is not used), but I am sure that there are more formal instances, and I am wondering what they might be.