only

Only is a capricious word. It is much given to deserting its post and taking its place next the verb, regardless of what it qualifies. It is more natural to say 'he only spoke for ten minutes' than 'he spoke for only ten minutes'. ... But it cannot be denied that the irresponsible behaviour of only does sometimes create real ambiguity. Take such a sentence as:

His disease can only be alleviated by a surgical operation.

We cannot tell what this means, and must rewrite it either:

Only a surgical operation can alleviate his disease (it cannot be alleviated in any other way).

or:

A surgical operation can only alleviate his disease (it cannot cure it).

The Complete Plain Words, 2nd edn. 1973

I tapped you on your arm with my stick yesterday.

Only I tapped you on your arm with my stick yesterday
-- nobody else hit you.
I only tapped you on your arm with my stick yesterday
-- I didn't hit very hard.
I tapped only you on your arm with my stick yesterday
-- I didn't hit anyone else.
I tapped you only on your arm with my stick yesterday
-- I didn't hit you anywhere else.
I tapped you on only your arm with my stick yesterday
-- I didn't hit you anywhere else.
I tapped you on your only arm with my stick yesterday
-- when did you lose your other arm?
I tapped you on your arm only with my stick yesterday
-- I didn't hit you with anything else.
I tapped you on your arm with only my stick yesterday
-- I didn't hit you with anyone else's stick.
I tapped you on your arm with my only stick yesterday
-- I'm thinking of getting a second stick.
I tapped you on your arm with my stick only yesterday
-- was it really that recent?
I tapped you on your arm with my stick yesterday only
-- I didn't hit you at any other time.

Stress can be used to resolve some potential ambiguity.

I only tapped you on your arm with my stick yesterday
-- I didn't hit very hard.
I only tapped you on your arm with my stick yesterday
-- I didn't hit you anywhere else.