well.. in Arabic we have 3 kinds of the verb: الفعل المضارع present tense الفعل الماضي past tense الفعل الامر command tense and i don't agree with the answer above cuz we consider كان و اخواتها- ان و اخواتها as افعال ناقصة و سميت بالافعال الناقصة لانها تدخل على الجملة الاسمية ( المبتدأ و الخبر) ولم تكتفي برفع المبتدأ لاتمام المعنى و لكنها تحتاج الى الخبر ليصح المعنى and i think Arabic language is completely different from other languages ... there is no aux. verbs in Arabic cuz we don't need them... for instance if we add not to English sentence we add aux. verb to carry the negation ... but in Arabic we use" حروف النفي" to made the negation such as : لم ) تسكن اختي في هذه الشقة ) = My sister (did (not)) live in this apartment. حروف النفي (لا , ما , لم , لما , لن و إن المخففة)** (لنْ ) تسکنَ أختي في هذهِ الشقةَِ = My sister (will (not)) live in this apartment. so if u wanna learn Arabic language (although ur native!!!) u have to know ... The key to understanding how Arabic grammar works is in its system of roots. cuz the meaning will change not only the word class " v. n. adj. adv." but ... the answer of ur question is that... we dont have aux. v. in Arabic but we have instead what we call "حروف " such as .. حروف الجر، حروف الجزم ، حروف النفي، النصب ... الخ which gives the meaning of the aux. v hope its clear to u...

i talk arabic like you,dont try to think there is auxillary verb ممكن ان واخواتها وكان واخواتها تكون فعل مساعد؟ ان يذهب كان يقول,اصبح يضحك you can tell me when you know