What are grammatical cases in Czech? What are declensions? And why do we even need them? It's actually pretty clever, have a look:
Every noun (a person, a place, an animal or a thing) can play various roles in a situation. It can play the main role and do something. Or conversely, it can be just passive and something can be done to it.
Let's have a look at the sentence:
ANNA IS WRITING A LETTER WITH A PEN.
Anna is the one who is actively doing something, she is the subject (nominative). The letter is passively receiving Anna's action (accusative). The pen is the means by which Anna is writing (instrumental).
In English, we express the role of a word with the word order (SUBJECT-VERB-OBJECT) and the prepositions. In Czech, in addition to this, we also use cases (together with prepositions) to show who is doing what to whom.
In practice this means that we change the form of the word, usually its ending, to indicate its function.
Nominativ: Jana píše dopis. Jana is writing a letter.
Genitiv: Jdu domů bez Jany. I'm going home without Jana.
Dativ: Jdu k Janě. I'm going to Jana.
Accusative: Vidím Janu. I see Jana.
Vocative: Jano! Hey, Jana!
Locative: Mluvím o Janě. I speak about Jana.
Instrumental: Jdu domů s Janou. I'm going home with Jana.
If we go through the various cases of a word, we say that we decline it. Once we do this, we get a table with all possible forms of the word, which is called a declension.
Learn more about how cases work in my video!