Learn Danish: Vi behøver ikke at købe tørt sand.

Sand is a neuter noun (an et word). In Danish, when an adjective describes an indefinite neuter noun, it must take a -t ending. So, tør becomes tørt.

Sand doesn't have an article like 'a' (et) here. Do adjectives always agree with uncountable mass nouns anyway?

Yes! Even though sand is an uncountable mass noun and stands alone without an article, the adjective must still match the noun's inherent gender. Because sand is an et word, it still triggers the neuter -t ending on the adjective.

Why do we need the word at before købe?

Unlike true modal verbs such as kan (can) or skal (must), the verb at behøve (to need) is a regular verb. When you follow it with another verb, you must use the infinitive marker at, making it at købe (to buy).

Why does ikke come right after behøver instead of at the end of the sentence?

In a standard Danish main clause, adverbs like ikke must be placed immediately after the first conjugated verb. Here, behøver is the conjugated verb, so ikke steps in before the rest of the verbal phrase (at købe tørt sand).