So, you’ve learnt quite a few Polish verbs and are feeling very pleased with yourself – then, you find out that almost every English verb is equal to two Polish verbs! Yes, we’re talking about the two aspects – essentially, whether an action has been completed or not. So, for example with the verb robić (to do, to make):
- Imperfective is robić – “Wczoraj robiłem zadanie, kiedy przyszedł kolega.” (yesterday I was doing my homework, when my friend came round) – thus, the homework didn’t get done and the imperfective expresses an uncompleted, unfinished action (often translated as a progressive tense in English with -ing, for example 'was going', 'is going', "will be going")
- Perfective is zrobić – “Wczoraj wieczorem zrobiłem zadanie, a potem czytałem książkę.” (Yesterday evening I did my homework and then read a book. – ah! the homework is done so the perfective is a completed, finished action (often translated as a simple tense in English, for example 'went', 'go' 'will go').
For more on aspects, see page 269 of the excellent A Grammar of Contemporary Polish for a more in-depth explanation; also there is a very good discussion in Wikipedia about Aspects in Slavic languages, which draws mostly on the Polish example. However, and this is the point of this and the couple of postings following here: there are NO CLEAR RULES defining which prefixes form the perfective verbs – so you just have to learn the perfective version of the imperfective verbs parrot-fashion. However, it does help to know that perfective verbs are formed by:
- adding a prefix
- changing the stem suffix
- a stem alternation and a change of the stem suffix
- having two completely different stems (!)
- verbs only having the imperfective form – no perfective, yaay...