Yūnus 10:13-14

"We destroyed the generations before you when they did wrong; their messengers had come to them with clear proofs, but they were not going to believe… · Then, after them, We made you successors in the earth — to see how you would act."

قُرُون — root ق-ر-ن: to be together, to be joined. Qarn — a generation living at the same time; and from this a stretch of time. The core of the word is "being together": those who are present in one and the same age.

خَلَٰٓئِف — the root خ-ل-ف: to come after. The plural of khalīfa. The word is from the same root as ikhtilāfu'l-layli wa'n-nahār in the sixth verse — the succession of night and day and the succession of the generations are related with the same word.

I record this as an observation about the wording, and its ground is the shared root.

And the word will occur once more in the sūra, in the seventy-third verse: of those saved with Noah, wa jaʿalnāhum khalāʾif. The two occurrences can be compared:

لِنَنظُرَ كَيْفَ تَعْمَلُونَ — "to see how you would act."

The sentence states a purpose, and the purpose is seeing. I record this as my own reading: the succession is given not as a privilege but as a subject of observation. To take the place, that is, is itself the test.

And what is asked is not how much but how: kayfa taʿmalūn. Not quantity but manner.

وَمَا كَانُوا۟ لِيُؤْمِنُوا۟ — "they were not going to believe". The same construction will return in the seventy-fourth verse: fa-mā kānū li-yuʾminū bimā kadhdhabū bihī min qabl. It is a repetition that can be verified within the sūra.