Conditional Sentences: idhā, law, lawlā

Arabic picks its if by how real the condition is:

• إذا for real or expected conditions, usually with a past verb: إذا جاء أحمد فقل له (if Ahmad comes, tell him). إن + past verb is also correct here.
• لو for unreal conditions: لو درست لنجحت (if you had studied, you would have passed).
• لولا + noun, 'if it were not for': لولا المطر لخرجنا (if it weren't for the rain, we would have gone out).

After إذا the result starts with فـ when it is an order, a future with سـ or a nominal sentence. After لو and لولا the result starts with لـ, or with لما when it is negative. إن can also take the jussive in both parts: إن تدرسوا تنجحوا (if you study, you will succeed).