“In” with the accusative means into, onto, against... it has the idea of forward motion, whereas “in” with the ablative denotes simply position, in or on.
What is ablative and accusative?
Ablative with prepositions
In the case of the first two, the accusative indicates motion, and the ablative indicates no motion. For instance, in urbe means "in the city"; in urbem, "into the city". In the case of super, the accusative means "above" or "over", and the ablative means "concerning".
What case is in Latin?
There are 6 distinct cases in Latin: Nominative, Genitive, Dative, Accusative, Ablative, and Vocative; and there are vestiges of a seventh, the Locative.
What is the ablative case used for in Latin?
The ablative after prepositions of place or time denotes location in place and time. This is to be distinguished from the accusative after the same preposition which indicates motion into, down under, toward, etc.