Why is を触れさせる rather than を触れる used here?

Question

1. 十香はその場に座ったまま、不思議そうな顔をして、唇に指を触れさせていた。 (The context is 十香 touched her lips with her finger.)

2. 顔に出ていただろうか。士道は自分の頰を撫でるように手を触れさせながら、誤魔化すように続けた。 (士道 touched his cheek with his hand)

I come across these uses of the causative form long time ago. I’m always wondering why を触れさせる is used, since 触れる can be a transitive verb, as in 彼は私の肩に手を触れた。Could you please explain why 触れさせる, rather than 触れる is used in these sentences?

Answer 1

As you mentioned, there are both "transitive" and "intransitive" 触れる (What is the difference between に触れる and を触れる?). The transitive 触れる is for touching as a result of somebody moving their body, like your example 肩に手を触れる. It describes an action under one's control, thus usually used when touching or non-touching is most meaningful in that movement. On the other hand, the intransitive one (e.g. 肩に手が触れる) relatively focuses more on the state being contacting in the action.

So, there are following possibilities why the writer preferred 触れさせる:

• to emphasize the fact of "keeping/maintaining touching" (or perhaps "continuously tapping" in your first example)
• to say "let them touch", which suggests the contact is fairly light, like the hand barely feels the skin
• just the writer's personal habit

Incidentally, as far as I image those situations correctly, I don't feel it comfortable to use the transitive 触れる either. Instead,

1. 十香はその場に座ったまま、不思議そうな顔をして、唇に指を当てていた（当て続けていた）。
2. 士道は自分の頰を撫でるように手を（すべらせ／動かし／当て）ながら、誤魔化すように続けた。