Explain the function of 'inna wa akhawatuha' (إن وأخواتها) and how they affect the case endings of the nouns within a sentence.

'Inna wa akhawatuha' (إن وأخواتها), translated as 'inna and its sisters,' are a group of particles in Arabic grammar that perform a specific function in nominal sentences (الجملة الاسمية). A nominal sentence typically consists of a subject (المبتدأ) and a predicate (الخبر), with the subject usually in the nominative case (مرفوع) and the predicate also in the nominative case. When 'inna' or one of its sisters enters the sentence, it *alters the case endingsof the subject and predicate. Specifically, 'inna' and its sisters *make the subject accusative(منصوب) and *keep the predicate nominative(مرفوع). The subject after 'inna' is referred to as 'ism inna' (اسم إن), and the predicate is referred to as 'khabar inna' (خبر إن). Each sister of 'inna' adds a slightly different nuance to the meaning of the sentence. Some of the key sisters of 'inna' include: 'أَنَّ' (anna - that), which is used to introduce a clause that serves as the subject or object of another verb; 'كَأَنَّ' (ka'anna - as if, it seems as though), which expresses comparison or resemblance; 'لَكِنَّ' (lakinna - but), which indicates contrast or contradiction; 'لَيْتَ' (layta - if only), which expresses a wish or desire; and 'لَعَلَّ' (la'alla - perhaps, maybe), which expresses hope or expectation. For example, the sentence 'الكتاب مفيد' (al-kitābu mufīdun – the book is useful) has both subject and predicate in the nominative case. If 'inna' is added, it becomes 'إن الكتاب مفيد' (inna al-kitāba mufīdun – indeed, the book is useful). Notice that 'الكتاب' (al-kitābu) changes to 'الكتاب' (al-kitāba) taking the accusative case ending (نصب), while 'مفيد' (mufīdun) remains in the nominative case.