“Time flies like an arrow. Fruit flies like a banana.”
This admirably compact joke turns on the way so many English words play different roles in different sentences, like acrobats rearranging themselves in a human pyramid.
In the first sentence, time is a noun. Flies is the verb. The two words are bound together in a proverb so old it was borrowed from Latin (tempus fugit). “Like an arrow” provides extra zing. The pattern is noun plus intransitive verb plus prepositional phrase.
At first glance, the second sentence seems to follow the same pattern.
But wait a minute: Fruit doesn’t “fly” like a banana. A banana is a fruit. And here, fruit is more like an adjective, modifying flies.
It can do that because flies isn’t a third-person singular verb, as in the first sentence. It’s a plural noun, subject of like, which was a preposition in the first sentence but is a plural verb in the second. The pattern of the second sentence is thus attributive noun (adjective) plus plural noun plus transitive verb plus direct object.
Not until you get to that direct object (“a banana”) does the whole thing make sense. You’ve been led down what linguists call “a garden path.”
A garden path sentence is “one that is exceptionally hard for the reader to parse,” as the grammar website Stacked Exchange notes.
Garden paths are of interest not only to comedians but to computer scientists in the field of natural language programming – Siri, do you understand what I’m saying? How can a mere bot make sense of “flies like a banana”?
But writers need to pay attention to garden paths, too.
Ordinarily, the goal should be to lead readers from one logical idea to the next. They should not have to carry on an inner dialogue (“oh, that must have been the main verb”) and keep reevaluating each word read in the light of what comes next, like a GPS device “recalculating, recalculating” when a driver turns unexpectedly.
A classic garden path sentence is “The horse raced past the barn fell.” It’s perfectly grammatical, but it will make a reader stumble.
As Stacked Exchange explains: “The ambiguous word is raced and the disambiguating word is fell.” When you get to “fell,” in other words, the little light bulb of meaning switches on. You realize “raced” wasn’t the main verb.
Better would have been, “The horse that was raced past the barn fell.” Or in a tight space: “The horse driven past the barn fell.” (“Driven,” unlike “raced,” can’t be mistaken for the predicate verb.)
You can have fun playing in the “garden” – just search online for “garden path sentences.”
But in the real world of workaday prose, you’ll want to remember that it can be a false economy to leave out commas, definite articles, and even “that” clauses that help make a sentence clear from start to finish.