Learn Finnish: Suvaitsevainen opettaja ymmärtäisi tottelevaista lasta. - A tolerant teacher would understand an obedient child.

They are formed by taking the present tense stem of the verb and adding the tendency suffix -vainen. For suvaita (to tolerate), the stem is suvaitse-, making suvaitsevainen (tolerant). For totella (to obey), the stem is tottele-, making tottelevainen (obedient).

Why does tottelevainen change to tottelevaista in this sentence?

It must match the partitive case of the noun it modifies, lasta. When a word ends in -nen, the partitive singular is formed by replacing -nen with -sta or -stä. Therefore, the suffix -vainen always becomes -vaista or -väistä in the partitive singular.

Why are tottelevaista and lasta in the partitive case to begin with?

The verb ymmärtää (to understand) is a partitive verb. Because understanding is considered an abstract, ongoing state of mind rather than a completed physical action, it almost always requires its object to be in the partitive case.

What gives ymmärtäisi the meaning of 'would understand'?