If I touch an item (like a book) intentionally, I might say
I touch the book.
Now, if this had happened without my being aware of it, I would not say that I touched it, but I also would not say that the book touched me.
How should I describe this situation?
You would also say I touched the book.
Although it's a strange thing to say, because what does it matter?
Books exist to be touched, after all, and especially to be read.
If it matters to you that it's accidental, say I touched the book accidentally.
Touch is a Sense Verb, and they have special syntactic affordances.
You're talking about the Volitional versus the Non-volitional varieties of sense verbs.
Volitional means something you do on purpose. Non-volitional means you did it accidentally.
It's the difference between spill and pour. English doesn't usually distinguish volitionality
in its active verbs. In some cases one can tell, and in others it doesn't matter.
But sense verbs are special. The long-distance senses, sight and hearing, both use different verbs
for volitional (listen, look) versus non-volitional (hear, see). They're all active verbs, and the non-volitional ones are transitive (He saw/heard her), but the volitional ones are intransitive, and require a preposition (He looked at/listened to her). The other senses are less distinctive.
If a book is sitting on a table, and you reach out and make contact with it, you do touch the book. But if the book is sitting precariously on the table, and falls off and makes contact with your leg as you walk by, without any action on your part, then, in theory, you could say that the book touched you. The problem with this is that "touch" has an alternative meaning relating to emotions, as Janus Bahs Jacquet explained, and the most likely conclusion one would reach if you told them the book touched you, is that you were emotionally moved by the book in some fashion.
So, the solution in this case is to choose another word. If the impact of the book on your leg was slight, you might use the verb "grazed", as in, "I'm all right; it only grazed me"; or if the impact was somewhat more forceful (or it was a large book), then you might use the verb "hit", as in "The book hit me; that hurts."
One alternative is to switch tense:
I suddenly realized that the book and I were touching.
This doesn't place any intent on either object involved (you or the book).
I believe the idea of touch sounds intentional alone, thus just adding an adverb would suffice, such as ... I accidentally/mistakenly touched the book.
It does sound slightly foreign in speech, using the word touch by accident, so perhaps refer to ...I accidentally knocked/brushed/moved the book.
Or switch perspective, and start I didn't realise that I had touched the book.
I brushed against the book
implies that I didn't purposefully touch the book. I may have felt it or not.
'Touch' gives the connotation, whether active or passive, of someone being aware of/feeling the touching.
