Rule 1: 1. Conditional sentences in advice and letters
Advice naturally takes the form of a condition followed by a command or a promise. Three shapes cover almost every case. Promise: إِنْ with two jussives, or إِذَا with two perfects: إِنْ تُرَاجِعْ دُرُوسَكَ تَنْجَحْ. Command or prohibition: the apodosis is an imperative or لَا + jussive, so it must open with فَ: إِذَا وَجَدْتَ مَسْأَلَةً صَعْبَةً فَاسْأَلْ عَنْهَا. Reassurance: a nominal apodosis, again with فَ, very often beginning with a pronoun: إِذَا أَرَدْتَ مُسَاعَدَتِي فَأَنَا فِي الْمَدْرَسَةِ كُلَّ يَوْمٍ. The particle أَمَّا as for may stand before إِنْ to mark a contrast: أَمَّا إِنْ لَمْ تَسْتَطِعِ الْحُضُورَ فَاكْتُبْ إِلَيَّ.
إِنْ تُرَاجِعْ دُرُوسَكَ كُلَّ مَسَاءٍ تَنْجَحْ فِي الِامْتِحَانِ.
in turājiʿ durūsaka kulla masāʾin tanjaḥ fi l-imtiḥāni
If you revise your lessons every evening, you will pass the examination.
Promise: jussive + jussive, no فَ.
إِذَا وَجَدْتَ مَسْأَلَةً صَعْبَةً فَاسْأَلْ عَنْهَا فِي الصَّفِّ.
idhā wajadta masʾalatan ṣaʿbatan fa-sʾal ʿanhā fi ṣ-ṣaffi
If you find a difficult problem, ask about it in class.
Command: فَ + imperative.
إِذَا أَرَدْتَ مُسَاعَدَتِي فَأَنَا فِي الْمَكْتَبَةِ بَعْدَ الظُّهْرِ.
idhā aradta musāʿadatī fa-ana fi l-maktabati baʿda ẓ-ẓuhri
If you want my help, I am in the library in the afternoon.
Nominal apodosis: فَ + pronoun.
أَمَّا إِنْ لَمْ تَفْهَمِ الدَّرْسَ فَلَا تَسْكُتْ عَنْ ذٰلِكَ.
ammā in lam tafhami d-darsa fa-lā taskut ʿan dhālika
But if you do not understand the lesson, do not keep quiet about it.
أَمَّا … فَ wrapped round a conditional with إِنْ لَمْ.
لَوْ سَهِرْتَ لَيْلَةَ الِامْتِحَانِ لَنَسِيتَ نِصْفَ مَا حَفِظْتَ.
law sahirta laylata l-imtiḥāni la-nasīta niṣfa mā ḥafiẓta
If you stayed up the night before the exam, you would forget half of what you had memorised.
لَوْ … لَـ: a warning about something that has not happened.