 If natural language were structurally unambiguous with respect to some comprehensive, effectively parsable grammar, our parsing technology would presumably have attained human-like accuracy some time ago, instead of levelling off at about 90% constituent recognition accuracy.  In fact, however, language is ambiguous at all structural levels: at the level of speech sounds (“recognize speech” vs.  “wreck a nice beach”); morphology (“un-wrapped” vs. “unwrap-ped”); word category (round as an adjective, noun, verb or adverb); compound word structure (wild goose chase); phrase category (nominal that-clause vs. relative clause in “the idea that he is entertaining”); and modifier (or complement) attachment (“He hit the man with the baguette”). The parenthetical examples here have been chosen so that their ambiguity is readily noticeable, but ambiguities are far more abundant than is intuitively apparent, and the number of alternative analyses of a moderately long sentence can easily run into the thousands.