Estonian has two infinitives, the so called -da infinitive (endings in -a, -ta, -da) and the -ma infinitive. Apart from having to know when to use the two infintive forms (on which I will post in the future) one needs to learn the form of the stem as this can be different between the two infinitives. In this post I want to discuss forming the Estonian gerund. The Estonian gerund is formed from the stem of the -da infinitive. It has three endings: -des, -tes, and -es.
-da ---- -des
laul/da 'to sing' ---- laul/des 'singing'
tööta/da 'to work' ---- tööta/des 'working'
-ta ---- -tes
joos/ta 'to run' ---- joos/tes 'running'
ooda/ta 'to wait' ---- ooda/tes 'waiting'
-a ---- -es
tull/a 'to come' ---- tull/es 'coming'
minn/a 'to go' ---- minn/es 'going'
Now let's look at some examples of how to gerund is used. The gerund in Estonian is used differently from how it operates in English. In English the gerund can be thought of as a verb used as a noun, e.g. speaking in: I like speaking Estonian. In Estonian the gerund is used to indicate some action that takes place at the same time as another. This is better understood by seeing the Estonian gerund in action. The gerund is marked in bold in the Estonian examples.
Me istume vaikides. 'We sit (while) being quiet'.
Süües tõuseb/ kasvab isu. 'While eating, the appetite increases'.
Õnnetus ei hüüa tulles. 'An accident does yell (to signal) that it comes'.
Laps tuleb joostes koju. 'The child comes running home'.
Lauldes ja mängides läheb aeg kiiresti. 'While singing and playing time passes quickly'.
Aeg läheb lennates. 'Time goes flying [Time flies]'.
Mida tühjem tünn, seda suurem on mürin sõites.
'The emptier the barrel, the bigger the rumble while travelling'.
Kord tänaval jalutades kuulen korraga, et keegi läheneb mulle selja tagant kiiresti joostes.
'Once on the street I suddendly hear while walking, that someone approaches from behind my back quickly running'.
For those interested in Estonian morphology from a diachronic perspective, the gerund originated from the inessive case (ending in -s) of the -da infinitive. This form was used to answer the questions kus? 'where' and milles? 'in/ at what?' No other case forms of the -da infinitive survive in the modern language.
Source: Estonian Textbook by Juhan Tuldava, 1994, pg. 137-138