Verbs that switch thematic roles, but not surface structure
I think you're talking about patientive ambitransitives. According to Wikipedia:
Patientive (S = O) ambitransitives are those where the single argument of the intransitive (S) corresponds to the object (O) of the transitive. For example, in the sentence John (S) tripped and John (A) tripped Mary (O), John is not the person doing the falling in both sentences.
Most of the time, ambiguity is resolved by the end of the sentence:
- The bat broke.
- The bat broke the window.
However, it is possible to make a really bad sentence that has ambiguity. Here's an example:
- John looks like he's trying to find something.
- John looks under the rug, like he's trying to find something.
- John seems like he's trying to find something
I would, however, say that a comma is required (after "looks") if you want the first interpretation. If spoken, there should be a pause there.
I can suggest one such ambiguous sentence, taken from Simon Fraser University linguistics professor DeArmond's page on instruments.
John felt cold.
This can mean one of two things:
That John is in a cold environment, and feels too cold, he doesn't have a warm enough coat. This makes him an experiencer and the cold is a state.
That John feels cold to another person's touch. DeArmond suggests that he is dead and the mortician feels that he is cold to the touch. This makes John a theme.
I am not an expert on thematic relations, but I would suggest another ambiguous sentence, but I'm open to feedback on my assignment of roles:
Mary shot the gun.
Here, Mary could have:
- Shot a gun at an unspecified third person; or
- Used a gun to shoot another gun.
The first reading suggests the gun is a theme and the second that it is an instrument.