Commands of weak verbs (قل، نم، امش، ضع)

Commands come from the jussive

Take the jussive you know from لم, drop the prefix, and you have the command: لم يقُلْ → قُلْ. A sound verb needs a helping ا in front (اكتبْ); most weak verbs do not.

Hollow verbs: قل، نم، زر

The long vowel shrinks, as after لم: قُلْ, نَمْ, زُرْ. Add an ending and it comes back: قولي, ناموا, زوري.

Assimilated verbs: ضع، قف، صل

The present has already lost the و (يضع، يقف، يصل), so the command is just two letters.

Defective verbs: امش، انس، ادع

These take the helping ا, and the masculine loses its final vowel letter, as in لم يمشِ: امشِ, انسَ, ادعُ — written امش، انس، ادع. The feminine ends in ي again: امشي، انسي، ادعي.

The negative command is the same short jussive after لا:

Two irregular commands: خذ، كل

أخذ and أكل drop their hamza: خُذْ take!, كُلْ eat!. Written without vowels, كل looks like كل every; the sentence shows which one it is.