人 - on'yomi ニン or ジン rule of thumb

Question

I sometimes have trouble figuring out what on'yomi 人 has in unfamiliar jukugo, and was wondering whether there was any kind of rule-of-thumb for figuring it out, assuming it is the only character whose reading is unknown in a compound.

Aside from cases such as the character sequence 人生 read 人{じん}生{せい} when treated as a complete word but 人{にん}生{せい} as part of the word 浪{ろう}人{にん}生{せい} due to it being being derived from rōnin+[gaku]sei, is there any way to tell which reading is used for a jukugo? Or is it only possible to tell if you know the etymology of the word and when the atomic jukugo entered Japanese due to the two waves of import of the classical Chinese reading njin?

Answer 1

• 人 following a place name is read as じん: 関西人, 韓国人, 宇宙人
• 人 following the name of a field or a social group is read as じん: 芸能人, 業界人, 社会人
• 人 following a number is read as にん: 三人, 五人
• 人 following a suru-verb is read as にん: 世話人, 商売人, 使用人, 苦労人, 通行人
• 人 following a na-adjective tends to be read as じん: 自由人, 有名人, 野蛮人 (exception: 貧乏人: 貧乏 is also a suru-verb, though)
• 人 following a native Japanese word (和語) is usually read as にん: 遊び人, 仕掛け人, けが人 (exception: 暇人【ひまじん】)

As for words starting with 人, the number of such words is not large and it may be best to memorize them individually.

Answer 2

Or is it only possible to tell if you know the etymology of the word and when the atomic jukugo entered Japanese due to the two waves of import of the classical Chinese reading njin?

I think this is the case and you virtually have to learn the proper reading(s) word by word. And there is also a 訓 reading and 連濁 like 村人.

It isn't much of a help, but 仏教用語 tend to have 呉音 reading.