إنَّ and its sisters are particles applied to the mubtada and khabar (subject and predicate) similar to كانَ but have the opposite grammatical effect – They give the accusative case to the subject and nominative case to the predicate.
These particles are:
إنّ verily, indeed
أنّ that
لكنّ but
لأنّ because
لعلّ perhaps
ليت if only
Examples:
إِنَّ اللَّهَ غَفُورٌ رَّحِيمٌ
Verily Allah is most forgiving most merciful
عرفتُ أنَّ الطالبَ مجتهدٌ
I came to know that the student is hardworking
رأيتُه ولكنّه مشغُولٌ
I saw him but he is busy
يا ليت الدرسُ يسيرًا
If only the lesson was easy