Casally modulated prepositions are prepositions where their meaning is modified by the grammatical case it is taking. The most common form of this type of preposition are bigovernate; that is they can take one of two cases.

There exist a reasonable number of bigovernate prepositions in German; these are an, auf, hinter, in, neben, uber, unter, vor and zwischen.[1] These prepositions can take either the accusative or dative grammatical cases. The accusative case is used when there is movement relative to the object with which the preposition agrees (e.g. I go into the cinema, "Ich gehe in das Kino") whereas the dative case is used when the subject of the preposition is static in relation to the object with which the preposition agrees (e.g. I am in the cinema, "Ich bin in dem Kino"), the difference here being between the definite article (das/dem). There are fewer bigovernate prepositions in Latin, the most common of which are in, sub, subter and super. These can take either the accusative or ablative cases. The meaning is modified in a similar way to German. If the preposition takes the accusative then it carries connotations of motion whereas if it takes the ablative then it suggests that the subject of the preposition is at rest. Compare "eram in horto" (I was in the garden) with "veni in hortum" (I came into the garden). Unlike German the difference between these two examples is expressed through the case-endings on the nouns (horto[ABL]/hortum[ACC]). It is much easier to distinguish between the two examples in Latin because the ablative endings are always different to the accuastive endings. It has been suggested that the use of the ablative in this way arose on account of the merging of the locative and ablative cases There are actually quite a few prepositions in Russian that are monogovernate, one such preposition being к 'towards' governing only the dative case. The great majority, if not almost all prepositions govern two or even three cases. As is the case in German and Latin, most spatial prepositions govern the locative case when there is no movement (some prepositions however govern the instrumental case). The same spatial prepositions govern the accusative case when their complement is the target of a movement.