Learn Finnish: Älkäämme koskaan aliarvioiko alamaisiamme. - Let's never underestimate our subjects.

It uses the first-person plural negative verb älkäämme (let us not). The main verb then takes its imperative stem and adds the suffix -ko or -kö. For aliarvioida (to underestimate), the stem is aliarvioi-, making it aliarvioiko. In everyday spoken Finnish, you would usually hear the negative passive instead: ei aliarvioida.

Why doesn't the word for 'never' have the negative word ei attached to it here?

The word koskaan needs a negative verb to mean 'never', but that negation is already provided by älkäämme. Finnish doesn't repeat the negative verb within the same clause, so älkäämme koskaan simply works together to mean 'let's never'.

Why is the object alamaisiamme in the partitive case?

There are actually two rules overlapping here to make it partitive! First, in any negative sentence, the object must be in the partitive case. Second, the verb aliarvioida inherently requires a partitive object anyway. The form here is the plural partitive alamaisia plus the possessive suffix -mme (our).

How does the base word alamainen change to become alamaisiamme?