Learn Finnish: Sata muurahaista rakentaa kekoa talveksi. - A hundred ants are building a mound for the winter.

This is the core rule for quantified subjects. When a subject is formed by a number and a noun in the partitive case (like sata muurahaista), the verb takes the third-person singular form. Finnish treats 'a hundred ants' as a single collective amount, so we use rakentaa instead of the plural rakentavat.

Why is muurahaista in the partitive singular instead of a plural form?

In Finnish, numbers greater than one require the following noun to be in the partitive singular. The dictionary form is muurahainen. For words ending in -nen, the partitive singular is formed by replacing -nen with -ista, giving us muurahaista.

Why is the object kekoa in the partitive case?

We use the partitive case for the object here because the action is ongoing and not yet complete. The ants are currently building the mound (keko). If we were talking about a completed action, the object would be in a total object case instead.

What grammar rule is being used in the word talveksi (for the winter)?

This is the translative case, marked by the -ksi ending. While often used to show a change of state, it is also used for time expressions to indicate a deadline or an intended time. Here, it shows that the mound is being prepared for the winter.