A. Some are primitive words, whose grammatical formation is not clear,
e.g. =nyt=, _now_; =heti=, _soon_; =aina=, _always_; =vielä=, _yet_;
=koska=, _when_.
B. A second class is formed by the addition of certain suffixes.
(1) Adverbs are formed from adjectives by the addition of =sti=, perhaps
related to the suffix of the elative, =sta=, e.g. =hywä=, _good_,
=hywästi=, _well_; =tietty=, _known_; =tietysti=, _certainly_. =lti=
is also found (cf. ablative =lta=); =laajalti=, _widely_, e.g. =se
on laajalti tunnettu=, _he is widely known_; =paksulta=, _much_ or
_thickly_; =syvältä=, _deeply_.
(2) =ten= or =ti= (cf. prolative =tse=) is added to pronouns. =Täten=,
_so_; =miten=, _how_; =siten=, _so_; =muuten=, _otherwise_; =peräti=,
_entirely_.
(3) =isin= (instructive) is added to nouns. =Maisin=, _by land_;
=takaisin=, _back_.
(4) =nne= is added to pronouns, and forms adverbs of direction. =Sinne=,
_thither_; =tänne=, _hither_; =minne=, _whither_; =jonnekunne=, _to
somewhere or other_.
(5) =tusten=, =tuksin=, =ksuttain=, =kkain=, are used to form
adverbs expressing a mutual relation. =Rinnatusten=, _side by side_;
=käsityksin=, _hand in hand_; =peräksyttäin= _or_ =peräkkäin=, _one
behind the other_.
(6) =oin=, or sometimes =ain= (probably from =ajoin=, =aika=, _time_),
is added to the adessive case of pronouns to form temporal adverbs.
=Silloin=, _then_; =milloin=, _when_; =muinoin=, _formerly_.