What is the difference between に触れる and を触れる?

Question

Example sentences:

手をふれないでください。

ボールはネットに触れた。

The second sentence feels like passive but then I would write it like this: に触れられる。

Answer 1

The verb 触れる{ふれる} is a little unintuitive in its usage. Strictly speaking it doesn't mean simply "to touch something" but rather "to touch something to something else". The thing being touched is always marked with the indirect object に, but the thing doing the touching can be marked with を, で or が with slightly different nuances.

The usage with を refers to a definite subject deliberately touching one thing to another thing. So AがYにXを触れる means "A touches X to Y". It's most commonly used with a body part as the direct object, such as 私はテーブルに指を触れた "I touched my finger to the table".

The usage with が can be thought of as a separate, intransitive verb that's fairly straightforward: XがYに触れる means "X touches Y". This is the pattern that's being used in your second example ボールはネットに触れた "The ball touched the net". (the が has been topicalised to は). With this form the touching doesn't have to be a deliberate action, but it can be - 私はテーブルに触れた "I touched the table" is perfectly acceptable.

The usage with で is a sort of halfway house between the others - for practical purposes it's essentially the same as the transitive usage with を (since there's an actor deliberately touching one thing with another), but grammatically it's an extension of the intransitive usage with が. 私は指でテーブルに触れた "I touched the table with my finger" expresses the same action as 私はテーブルに指を触れた "I touched my finger to the table", but the emphasis is subtly different.

To complicate things, there's also a completely separate verb 触る{さわる} which uses the same kanji but has completely different usage patterns. This verb is more intuitive, and can use either に or を to indicate the thing being touched. So 指を触る{さわる}, 指に触る{さわる} and 指に触れる{ふれる} all mean essentially the same thing (the finger is what's being touched) but 指を触れる{ふれる}, 指で触れる{ふれる} and 指で触る{さわる} mean the opposite (the finger is what you're doing the touching with).