In general, as discussed earlier, there may be many different parses for a complex sentence, as the grammar rules and dictionary allow the same list of words to be parsed in several different ways. A commonly cited example is the pair of sentences:
``Flies'' can be either a verb and a noun, while ``likes'' can be either a verb and a preposition (or whatever). So, in the first sentence ``Time'' should be the noun phrase and ``flies like an arrow'' to be the verb phrase (with ``like an arrow'' modifying flies). In the second sentence ``Fruit flies'' should be the noun phrase and ``like a banana'' to be the verb phrase. Now, WE know which is the ``right'' parse because we know that there is no such thing as a ``time fly'' and it would be a bit strange to ``fly like a banana''. But without such general knowledge about word meanings we coudn't tell which parse is correct, so a parser, with no semantic component, should return both parses, and leave it up to the semantic stage of analysis to throw out the bogus one.