Kana and its sisters are verbs when placed as head constituents of a nominal sentence, put the information/predicative complement (الخَبَر) in the accusative case (مَنْصُوب); this is opposite to ‘Inna and its sisters’. 

The verb كانَ originally means ‘to be’. Because the nominal sentence (الجُمْلة الاسمية) doesn’t note the tense in Arabic, we need to precede it with the verb كانَ (= to be) as a temporal exponent if we want to place it clearly in the past.

According to Arabic grammarians, a verb is an action correlated to a tense. Kāna is mainly used as a complement to time and lacks the ‘action’ condition. For that very reason, it is not considered to be fully a verb in Arabic even though it has its own conjugation. 

Henceforth, when كانَ is put as the head constituent of a nominal sentence, the sentence doesn’t become a verbal sentence but the subject (المُبْتَدأ) following it is then called اِسْم كانَ (noun of kāna) and remains in the nominative case (مَرفُوع), while the predicate called خَبَر كانَ (predicate of kāna) turns into the accusative case (if it is a noun or an adjective).  

Kāna time values 

Depending on its use كانَ can express several nuances in the tenses which their English equivalent would be:

1. Past tense as a head constituent of a nominal sentence (الجُمْلة الاسميّة):

Example	Construction
كانَ الطَقْسُ مُشْمِسًا و حارًّا فِي الصَبْاحِ  The weather was sunny and hot this morning	كانَ + جُمْلة اسمية

2. Past progressive or past habitual followed by a verb in the imperfect (present) indicative tense ( المُضارِع المَرفُوع):

Example	Construction
كُنّا نَخْرُجُ من الجامِعةِ We were getting out of the university	كانَ + المُضارِع المَرْفُوع

3. Pluperfect when followed by a verb in the perfect (past) tense (الماضي):

Example	Construction
كانَتْ قَدْ اِسْتَعَدَّتْ لِعَرْضِها She had prepared for her presentation	كانَ + قَدْ + الماضي

4. Future perfect when put in the future tense followed by a perfect (past) tense verb (الماضي):

Example	Construction
سأَكُونُ قَد جَلَسْتُ قَبْلَ أَنْ يَتَكَلَّمَ المُعَلِّمُ I will have sat down before the teacher speaks	سَ+ يَكونُ + قَدْ + الماضي

Note: If the subject (المُبْتَدأ) was a detached pronoun, in the nominal sentence without كان, it will be implied in the temporal exponent conjugated كانَ.

كُنّا مُرْهَقِينَ We were exhausted

? نَحْنُ مُرْهَقُونَ We are exhausted

Kāna’s conjugation / تَصْريف كان

Perfect tense / الماضي

مُثَنّى (dual)	جمع (plural)	مُفْرَد (singular)	الماضي Perfect tense
كُنّا		كُنْتُ	المُتَكَلِّم  1st person
كُنْتُما	كُنْتُم	كُنْتَ	المُذَكَّر masc.	المُخاطَب  2nd person
	كُنْتُنَّ	كُنْتِ	المُؤَنَّث fem.
كانَا	كانُوا	كانَ	المُذَكَّر masc.	الغائِب  3rd person
كانَتا	كُنَّ	كانَتْ	المُؤَنَّث fem.

Imperfect indicative tense / المُضارِع المَرْفوع

مُثَنّى (dual)	جمع (plural)	مُفْرَد (singular)	المُضارِع المَرْفوع Imperfect indicative tense
نَكُونُ		أَكُونُ	المُتَكَلِّم  1st person
تَكُونانِ	تَكُونُون	تَكُونُ	المُذَكَّر masc.	المُخاطَب  2nd person
	تَكُنَّ	تَكُونِينَ	المُؤَنَّث fem.
يَكُونانِ	يَكُونُون	يَكُونُ	المُذَكَّر masc.	الغائِب  3rd person
تَكُونانِ	يَكُنَّ	تَكُونُ	المُؤَنَّث fem.

Kana’s sisters

We usually divide kāna and its sisters into three separate categories:

• Complete verbs / أفعال تامة التصرف: those are the verbs that exist in all three conjugation tenses in Arabic, perfect, imperfect, and imperative.

• Incomplete verbs / أفعال ناقصة التصرف: those are the verbs that only exist in the perfect and imperfect tenses.

• Frozen verbs / أفعال جامدة: those are the verbs that only exist in the perfect tense.

أَفْعال جامِدة Frozen verbs	أَفْعال ناقِصة التَصَرُّف Incomplete verbs	أَفْعال تامّة التَصَرُّف Complete verbs
لَيْسَ nominal sentence negation	ما زالَ to still do /to continue to do	كانَ to be
		صارَ to become
		أَصْبَحَ to become
ما دامَ as long as	ما بَرِحَ to still do /to continue to do	ظلَّ to still do /to continue to do
		باتَ to become
ما ظَلَّ as long as	ما اِنْفَكَّ to still do /to continue to do	أَمْسَى  to become
	ما فَتِئَ to still do /to continue to do	أَضْحى  to become

✨ Try out the automatic verb conjugator here

Note: At the exception of كانَ all the complete verbs also have a 2nd original meaning when not used as a temporal exponent.

Note 2: The incomplete verbs (الأَفْعال الناقِصة التَصَرُّف) are translated as ‘to cease’, ‘disappear’, and/or ‘go away’. When accompanied by the negative particle ما in the perfect tense, or لا in the imperfect tense, they mean “is still (doing)” and/or “continues to (do)“. Both tenses have an identical significance.

لا يَزالَ يَدْرُسُ في الجامعةِ He’s still studying at university	ما زالَ يَدْرُسُ في الجامعةِ He’s still studying at university
لا تَنْفَكَُ تَعْمَلُ في اللَّيْلِ She’s still working at night	ما اِنْفَكَّتْ تَعْمَلُ في اللَّيْلِ She’s still working at night
لا نَبْرَحُ المَكانَ We are still in place	ما بَرِحْنا المَكانَ We are still in place

Note 3: The ما used for frozen verbs (الأَفْعال جامِدة) isn’t the negative particle used for incomplete verbs but rather the relative particle.

I will work as long as I live	سَأَعْمَلُ ما دُمْتُ حيًّا
She will disturb us as long as she stays in our house	سَتُزْعِجُنا ما ظَلّتْ في بَيْتِنا