Breakdown of Der Rucksack liegt unter dem Tisch.
der Tisch
the table
der Rucksack
the backpack
liegen
to lie
unter
under, below
Questions & Answers about Der Rucksack liegt unter dem Tisch.
Why does the sentence use dem Tisch instead of der Tisch?
In this sentence, the backpack is in a fixed location. The preposition unter (under) is a 'two-way' preposition. When these prepositions answer the question 'Where?' (Wo?), they require the dative case. Since Tisch is a masculine noun (der Tisch), it changes to dem Tisch in the dative case.
Could I just say ist instead of liegt?
Yes, Der Rucksack ist unter dem Tisch is perfectly fine and grammatically correct. However, German speakers love to be specific about how an object is positioned. Since a backpack usually rests flat on the ground, they often use liegen (to lie) to describe its location instead of just saying 'is'.
Will unter always use the dative case like it does here?
Not always! The word unter is a two-way preposition. We use it with the dative case here because the backpack is already resting in one place. If someone were moving the backpack to a spot under the table (answering 'To where?' or Wohin?), unter would take the accusative case instead.
Because it says dem Tisch, how do I know if the noun is masculine or neuter?