Verb. Imperfect (Simple Past)

The marker of the imperfect is -si or -i. The affirmative forms of the imperfect are conjugated.

The affirmative forms with the imperfect marker -si are formed from the stem of the -ma infinitive by adding the imperfect marker and the personal ending.

When the -ma infinitive marker is preceded by a consonant, the 3^rd pers. sg. imperfect marker -s is preceded by -i, e.g. ostma 'buy' > ostis, võtma 'take' > võttis , andma 'give' > andis.

The negative forms with the imperfect marker -si are not conjugated. The negative forms (ei + -nud participle) are formed from the -da infinitive stem.
ooda/ta > (ma, sa, ta, me, etc.) ei ooda/nud

 The imperfect marker -i occurs:
a) in some verbs with two-syllable stems where the marker of the -ma infinitive is preceded by -e e>i
tulema 'come' >

olema > olin, panema 'put' > panid, surema 'die' > suri
pesema 'wash' > pesime, tegema 'do' > tegite, nägema 'see' > nägid

 b) in verbs with one-syllable stems ending with a long vowel
aa + i > ai saama 'get' > sain
ää + i > äi jääma 'stay' > jäin
öö + i > õi sööma 'eat' > sõin; lööma 'hit' > lõin
oo > õi jooma 'drink' > jõin; tooma 'bring' > tõin; looma 'create' > lõin

The negative forms of the imperfect are composed of ei + -nud participle, but the -nud participle of verbs with the imperfect marker -i are irregular.