Most Finnish grammars are particularly easy to understand on this point. The basic idea is: In Finnish the direct object (commonly called the accusative object) may occur in the nominative, the genitive, or the partitive case. In order to make things easier to understand, nominative and genitive are called accusative. There is also a real accusative which is not called anything at all. Utmost care must be applied when interpreting the grammatical terminology. If you encounter the word 'accusative,' it can mean nominative or genitive, but never the real accusative. The term 'nominative' can mean accusative or, possibly, nominative. 'Genitive' can mean accusative or simply genitive, while partitive is always called partitive, although it may be accusative.