Kāna is interpreted in five ways:
1. Kāna is used in the sense of yanbaghī (it befits / is appropriate); when used with lā (lā yanbaghī), it means 'it does not befit / is not appropriate'; as in the following verses:
It is not for any human being [mā kāna = it is not / it is not possible, {i.e., lā yanbaghī = it does not befit / is not appropriate}] that Allah should give him the Scripture, authority, and prophethood and then he would say to the people, "Be servants to me rather than Allah." (Āl ʿImrān 3:79)
It is not for a believer [mā kāna = it is not / it is not possible, {i.e., lā yanbaghī = it does not befit / is not appropriate}] to kill another believer except by mistake. (al-Nisāʾ 4:92)
It is not for us to say this [mā yakūnu = it is not / it is not possible for us, {i.e., lā yanbaghī = it does not befit / is not appropriate for us}]. (al-Nūr 24:16)
There are many similar statements.
2. Kāna is used in speech as a ṣila (a connecting word without independent meaning); as in the following verses:
And Allah is over all things competent. (al-Aḥzāb 33:27)
Here, kāna is a ṣila in the speech. Thus, the phrase wa kāna Allāhu ʿalā kulli shayʾin qadīr means wa Allāhu ʿalā kulli shayʾin qadīr.
And Allah is Knowing and Wise. (al-Nisāʾ 4:111; al-Fatḥ 48:4)
Here, kāna is a ṣila in the speech. Thus, the phrase wa kāna Allāhu ʿalīman ḥakīman means wa Allāhu ʿalīmun ḥakīmun.
And Allah is Hearing and Seeing. (al-Nisāʾ 4:134)
Here, kāna is a ṣila in the speech. Thus, the phrase wa kāna Allāhu samīʿan baṣīran means wa Allāhu samīʿun baṣīrun.
And Allah is Forgiving and Merciful. (al-Nisāʾ 4:100)
Here too, kāna is a ṣila in the speech. Thus, the phrase wa kāna Allāhu ghafūran raḥīman means wa Allāhu ghafūrun raḥīmun.
3. Kāna is used in the sense of huwa (he is); as in the following verse:
How can we speak to one who was (kāna, i.e., huwa: he is) a child in the cradle? (Maryam 19:29)
4. The word kāna is interpreted as 'thus is/was'; as in the following verses:
Indeed, he (i.e., Ismāʿīl) was true to his promise [kāna]; and he was a messenger and a prophet [kāna, i.e., likewise kāna]. (Maryam 19:54)
Here, kāna means 'thus he was.' He used to enjoin upon his people prayer and zakat. (Maryam 19:55)
Before them, there was a king [kāna] who seized every good ship by force. (al-Kahf 18:79)
This statement also reports something that happened and passed in the past.
5. Kāna is used in the sense of ṣāra (to become); as in the following verse describing the attitude of Iblis when Allah commanded him to prostrate to Adam, and in the other verses below:
Iblis refused, was arrogant, and became one of the disbelievers [kāna]. (al-Baqara 2:34)
That is, Iblis, in Allah's knowledge, became a kāfir (disbeliever) by abandoning prostration to Adam—saying to his Lord: I will not be one to prostrate to a human being (al-Ḥijr 15:33); that is, I am better than him; therefore, it does not befit / is not appropriate for someone like me to prostrate to someone like him.
The sky will be opened and will become gates [fa-kānat abwāban, i.e., fa-ṣārat abwāban], and the mountains will be set in motion and become a mirage [fa-kānat sarāban, i.e., fa-ṣārat kal-sarāb]. (al-Nabaʾ 78:19–20)
The mountains will become [fa-kānat al-jibālu, i.e., fa-ṣārat al-jibālu] like drifting sand {i.e., like a heap of sand when stirred and set in motion}. (al-Muzzammil 73:14)
When they become scattered dust {i.e., when the mountains become like the dust particles seen when sunlight enters through a window}. (al-Wāqiʿa 56:6)
On that Day, the sky will be like molten metal {i.e., taṣīru al-samāʾ}, and the mountains will be like carded wool {i.e., kal-ṣawf al-manfūsh}. (al-Maʿārij 70:8–9)