Learn Arabic (Modern Standard): متى تسافر ليلا تهتد بالنجوم. - Whenever you m travel at night, you are guided by the stars.

Here, متى is used as a temporal conditional particle meaning 'whenever.' In this role, it sets up a condition and a result, and it forces both the condition verb (تسافر) and the result verb (تهتد) into the jussive case (majzoom).

The normal present tense form for 'you are guided' is تهتدي. Why is the final ي missing in تهتد?

Because متى forces the result verb into the jussive case. For 'defective' verbs that end in a weak letter, the jussive case is marked by completely dropping that final weak letter. You are left with تهتدِ, and the kasra under the د acts as a phonetic hint that a ي was dropped.

Does the first verb تسافر also show a jussive marker?

Yes! Since تسافر is a regular 'sound' verb that does not end in a weak letter, its jussive marker is simply a sukun (no vowel) on the final letter, making it pronounced as تسافرْ.

Why does the word for night, ليلا, take the accusative 'an' ending?

It is acting as an adverb of time. In Arabic grammar, words specifying the time or place an action occurs are put into the accusative case (mansub), which is marked here by the tanween fatha ending.

What verb form is تهتد and how does it change the root meaning?