Given our shared general assumptions about the world, you probably arrived
at an image rather like ours. This image relates to the following grammatical
parsing (analysis) of the sentence:
S
P
O
A
Mary |
kissed |
the boy |
on the nose.
But the sentence is actually grammatically ambiguous,
leading to two different understandings (or 'readings') of it. Let's
make the alternative meaning obvious by adding a bit more context.
Mary kissed the boy on the nose. But the
nose sneezed and the boy fell off.
'Groan!', we hear you say! But there is a point. This contextualisation
would lead to a different picture for the first sentence, as well as subsequent
pictures for the second sentence.
It would also lead to a different parsing of the
sentence:
S
P
O
Mary |
kissed |
the boy on the nose.
The prepositional phrase 'on the nose' is no longer an
immediate constituent of the sentence but a subpart of the noun phrase
acting as the object of 'kissed'. It is a complex post-modifier of the
head noun 'boy', helping to specify which boy it was that Mary kissed.
Although the example is a bit 'groany', you should be able to see that
we can use grammatical analysis to explain some ambiguities in sentences.
If we wanted to avoid the ambiguity we would have to change the structure,
for example to:
S
P
O
Mary |
kissed |
the boy who was standing on the
nose.
Now only the silly reading is possible. But to achieve the
disambiguation we have had to use a more complex structure. The above
sentence now has a clause embedded/nested inside the noun phrase,
post-modifying 'boy' (we use 'clause' to refer to the parts of complex
sentences which themselves have the kind of internal structure we have
seen in very simple sentences). The clause 'who was standing on the nose'
has the structure SPA. Clauses post-modifying the head nouns of noun phrases
are usually called relative clauses (because they 'relate' to the
head noun). Some traditional grammars called them adjectival clauses (because
they modify the head noun in noun phrases, as adjectives prototypically
do).
In the above example, the nested clause is part of a phrase,
and it is the whole phrase which is a constituent (the object) of the
sentence. But it is also possible for clauses to function on their
own as constituents of simple sentences or clauses. Consider the following
two sentences, which clearly have the same overall structure:
S
P
O
John |
wants |
Mary's love
John |
wants |
to be loved by Mary
The object in the first sentence is a noun phrase, but the
object in the second sentence is a clause, having the internal structure
PA.
