The article must match the grammatical gender of the noun. In Flemish like in German the three genders masculine, feminine and neuter are about equally common. In Standard Dutch, masculine and feminine have been merged into the so-called common gender, which is therefore twice as common as neuter gender.
- het paard, de paarden - neutral gender
- de vogel, de vogelen - common gender
This is why you should always learn the definite article along with every Dutch noun.