Most wonderful all are ... [sentences], and how they friends one with another.
O. Henry
Sentences may be related in various ways. For example, they may have the sama phrase structure, differing only in their words, which accounts for their differing meaning. We saw this earlier in sets of sentences such as The boat sailed up the river, A girl laughed at the monkey, and so on.
Two sentences with different meanings may contain the same words in the same order, differing only in structure, for example, The boy saw the man with the telescope. These are cases of structural ambiguity.
Two sentences may differ in structure, possibly with small differences in grammatical morphemes, but with no diference in meaning :
The father wept silently.
The father silently wept.
The astronomer saw a new galaxy with his telescope.
With his telescope the astronomer saw a new galaxy.
Mary insulted Bill
Bill was insulted by Mary
I know that you know
I know you know
Two sentence may have structural differences that correspond systematically to meaning difference.
The boy is sleeping.
Is the boy sleeping ?
The boy can sleep.
Can the boy sleep ?
The boy will sleep.
Will the boy sleep ?
The man is in the house.
Is the man in the house ?
The difference in the position of the verbal element is, can, will, corresponds to whether the sentence is declarative or inerrogative.
Phrase structure rules account for much syntactic knowledge, but they do not account for the fact that Mary insulted Bill has the same meaning as Bill was insulted by Mary, but a different meaning from Mary was insulted by Bill. Nor do they account for the systematic difference between statements knowledge, we must look beyond phrase structure rules.
