The most common verb olla (to be) is used as an auxiliary verb in different constructs, so that the meaning depends on the form of the main verb (content verb). Using the forms olen (I am) and olin (I were) and the verb ostaa (to buy), we can form the following constructs, to be described in detail in later sections:
This verb has mostly regular inflection, with ole- as the inflection stem, but irregular third person forms in present tense (on, ovat) and the stem liene- in the potential mood.
The verb tulla (to come; to become) is used as an auxiliary verb in two ways:
This verb has regular inflection, with tule- as the inflection stem.
The verb tehdä is not an auxiliary verb but mainly corresponds to “to do” and “to make”. So the verb refers to actions in general, e.g. Mitä teet? (What are you doing?), but also to producing something, e.g. Teen kakkua (I’m making a cake).
However, tehdä is also used as a generic verb referring to a previously used verb when imitating English (and Swedish) usage. It used to be normal to repeat a verb when needed, e.g. Ostin uuden auton, ja niin osti naapurinikin, but nowadays people often use a form of tehdä (such as teki “did”) instead: Ostin uuden auton, ja niin teki naapurinikin (I bought a new car, and so did my neighbor).
This verb has regular inflection, except that the vowel stem is teke- (strong grade) ∼ tee- (weak grade) but the consonant stem is teh-.