Questions & Answers about Ona zaczęła czytać nową książkę.
Why is zaczęła (perfective) used here instead of the imperfective zaczynała?
In Polish, verbs for starting and finishing are usually perfective when talking about a single, completed event in the past. Even though reading takes time, the act of starting the book is a one-time completed action.
Why do we use the imperfective infinitive czytać instead of the perfective przeczytać?
After verbs meaning "to start," "to finish," or "to continue" (like zacząć), you must always use an imperfective infinitive. This is because you are focusing on the ongoing process of reading that has just begun, not on the completion of the action.
Why is it nową książkę instead of the dictionary form nowa książka?
It is in the accusative case because it is the direct object of the verb czytać (it answers "what is she reading?"). For feminine singular words in this case, the adjective ending changes to -ą (nową) and the noun ending changes to -ę (książkę).