In fancy language, the accusative (biernik) case is perhaps best known as 'the case of the direct object'. The 'direct object' is a noun or a pronoun that follows particular verbs known as 'transitive verbs', which is a verb that requires an object. Don't worry, I promise that sounds harder than it is!
In simpler words, we use the accusative case in Polish to show what particular thing (a noun or pronoun) is being acted upon in a sentence.
There are also a number of other uses for the accusative case which we will touch on here, but for now it is safe to say that the central usage is as the case for the direct object, and, if you can tackle this, your grammar will improve substantially.
As in all Polish cases there are a number of declensions (ending changes to words) unique to the masculine, feminine and neuter plurals and singulars in the accusative case. Once you have studied these, there is really no substitute for practicing examples that will help you make these case changes off the cuff, and prepare you for the few exceptions to the rule associated with the accusative.
Uses of the Accusative
As we have already seen, the central usage of the accusative is to define the direct object. However, there are a number of other instances where the accusative is required that are worth remembering.
For example, it is always used for nouns coming after some prepositions, but only when these prepositions follow certain verbs (pytać o... (ask about), patrzyć na (look at)). It is also used to express duration of time, and for the nouns/adjectives following certain prepositions without verbs.
Accusative Endings (for nouns and adjectives)
The accusative actually makes four distinctions in terms of gender, instead of the usual three (masculine, feminine and neuter) adopted by polish case rules. Here we have a separate rule for masculine animate (essentially people and animals), masculine inanimate, feminine and neuter. Contrary to what you may be thinking, this distinction can actually make things easier, as there is actually no change for masculine inanimate nouns or neuter nouns in the accusative; their endings always stay the same.
Masculine animate nouns in the accusative add the ending -a, and their corresponding adjectives add the ending -ego.
For example, the sentence "I have a good cat", would read "mam dobry kot", if we wrote it using the nominative case. But, because 'mam' (I have) is a transitive verb, its object, the 'dobry kot' (good cat), needs to be in accusative: Mam dobrego kota.
All feminine nouns in the accusative change their -a ending to -ę, while their corresponding adjectives change their ending to -ą.
Let's use a similar example. "I have a pretty daughter" would read "mam piękna córka" if we wrote it in the nominative. But, in the correct accusative case, the sentence is transformed to, 'mam piękną córkę.
As we have already said, there are absolutely no changes needed when using masculine inanimate nouns, or neuter nouns in the accusative case. So, a sentence like "I love my town", reads "Kocham moje miasto" in both the nominative and accusative, because the noun miasto (town) is neuter.
Plurals
It's best to concentrate on memorizing the singular rules first and then moving onto the plurals, which are, briefly, as follows:
For masculine personal nouns the ending -ów is used (studentów (students)) while all other masculine plurals follow the same rule as the nominative.
For feminine plurals the ending is -y (dziewczyny (girls)), while neuter plurals have the ending -a: drzewo (tree) becomes drzewa (trees).