Learn Finnish: Taiteilijan on helppo havainnoida ihmisiä. - The artist finds it easy to observe people.

This sentence uses an experiential structure. Phrases expressing that something is easy, difficult, or necessary for someone (using phrases like on helppo, on vaikea, or on pakko) require the person experiencing it to be in the genitive case. Literally, the structure reads as "Of the artist is easy".

Why is the verb havainnoida in the 1st infinitive?

The 1st infinitive (the basic dictionary form) is required after the [Genitive] + on helppo structure. In this sentence pattern, the infinitive actually acts as the subject of the sentence, so the grammar literally translates to "To observe people is easy for the artist."

The verb havainnoida looks related to the noun havainto (an observation). How is it formed?

Finnish frequently uses the -oida or -öidä suffix to turn nouns into verbs, often implying a continuous, systematic, or professional action. Here, the root of the noun havainto is combined with this suffix to create the verb havainnoida (to observe).

Why is the object ihmisiä in the partitive plural?

Two rules point to the partitive here. First, havainnoida is an irresultative verb; observing is an ongoing process without a definitive completion point, which requires a partitive object. Second, the artist is observing an undefined amount or general mass of people, which triggers the partitive plural.