This little ‘semantic nut’ in English is an illustration of how we sometimes need more than just syntax and semantics to parse a simple sentence. Here are two sentences:
- People buy hybrids because they don’t pollute.
- People buy hybrids because they want to save fuel.
The structure of each is similar, and the word they clearly refers to a noun phrase in the earlier part of the sentence, either people or hybrids.
In the first case, we infer that they refers to the hybrids, not the people, although we know that both can pollute, of course.
In the second case, we infer that they refers to the people, not the hybrids, because it is the people who are able to save fuel, not the hybrid vehicles.
We thus choose between the possible referents of they on the basis of world knowledge, not syntax or semantics.
Although not an example of one, if you find this tantalising, you may enjoy a mind-bending acquaintance with Donkey sentences, another problem for the syntactic and semantic interface. There is an extensive literature on Donkey sentences, much of which is thoroughly opaque.
I acknowledge Mark Steedman’s challenging book “Taking Scope: the Natural Semantics of Quantifiers”, MIT Press, 2012, as the source of this ‘nut’. If you ever think that life is boring and lacks challenges, this is the book to start reading.