As an alternative to a predicative, as in Opettaja on sairas (The teacher is sick), we can sometimes use a predicative adverbial in Finnish: Opettaja on sairaana. The use of the essive (-nA case) makes it clear that a temporary state, not a permanent property, is referred to.
However, most simple expressions of being in a state do not make such distinctions. For example, we say Olen väsynyt; a predicative adverbial (väsyneenä) cannot be used here. In addition to a few adjectives like sairas, nouns in the essive form can be used as predicative adverbials, e.g. Olen täällä turistina (I am here as a tourist).
In general, a predicative adverbial characterizes the subject, the object, or an adverbial, often describing temporary state. They can be used with different verbs. In addition to the essive, predicative adverbials use the translative (-ksi case), the ablative (-ltA case), or the allative (-lle case). Examples: Opettaja tuli sairaaksi (The teacher became sick), Tämä leipä maistuu hyvältä ∼ hyvälle (This bread tastes good).
Predicative adverbials have special rules for the use of plural, e.g. Kaikki opettajat ovat nyt sairaana ∼ sairaina (All teachers are sick now).