Powerset

One morning back in grad school I was sitting in Cafe Milano on Bancroft Avenue in Berkeley, reading the campus newspaper, the Daily Cal. In true Berkeley form, in the 70’s the newspaper’s staff had rebelled and taken the paper off-campus, away from the control of university officials. Along with being anti-authority, the paper also didn’t seem to appreciate overzealous copy editing. While reading it that morning, I came across the following sentence:

The complex houses married and single students and their families.

Did you have trouble understanding this sentence? I must have stared at it for 5 minutes before it made sense to me. This is what linguists call a Garden Path Sentence, after the expression "leading someone down the garden path," meaning to deceive. The idea is the garden path is very pleasant, so the person being lead down it is distracted and doesn’t realize that they are being deceived. (My former officemate Dan Jurafsky included this example in his textbook Speech and Language Processing; it’s now something of a classic.) Let’s analyze why this sentence is so confusing. When you first start reading it, you see the word The which is a common way to start a sentence in English, and usually signals that the words that follow will be a noun phrase (a sequence of adjectives followed by nouns). Next you see complex, and since this word is most often used as an adjective, and since you saw the word the right before it, you’re very primed to think it’s an adjective. You then see the next word, houses, which is a perfectly fine, very common plural noun. So all is well, you’re reading a simple noun phrase, although it is a bit strange, since houses are usually described as large or charming or decrepit, but not complex. And then the kicker – you see married which is usually a verb, but houses never get married! Now you have to back up and see what went wrong. If you stare long enough you will probably realize that this sentence is talking about housing complexes that bored students … sorry, that board students, of both the married and single variety. You can make your own garden path sentences by following a few simple heuristics – this is how I made the title for this post. The trick is to choose words that can act as both nouns and verbs, or as both adjectives and nouns, words like store, search, and post. Then follow the ambiguous word by another word that can take on more than one form. The hard part is to then add on another noun phrase that makes sense with the less common interpretation of the second word. So in my example, Search Engines Leaking Oil for Holes, I intend you to interpret the first two words in their most common interpretation, as a plural noun-noun compound, search engines. I then take advantage of the fact that search can be both a noun and a verb, and add the verb leaking to change the meaning to be search a leaking engine. I then tack on the rest to complete the sentence. Another one I came up with this way is:

Blog Posts Digest Stories

The idea here is that posts when modifying blog has come to mean the outcome of posting something to a blog, so it’s closely related to the verb form of posts. I then tack on digest which is also both a noun and a verb representing similar concepts. The nominal form "digest" can be thought of as the outcome of someone reading a lot of articles, metaphorically "digesting" them, and producing a shortened list. So blog posts digest stories is kind of a double-entendre. I’ll close with a challenge for Powerset fans: how hard would it be to come up with an automatic garden-path sentence generator?

-Marti Hearst

*Editor’s Note: Marti is a professor at Berkeley in the very cool School of Information and a consultant at Powerset. All opinions expressed are more or less hers. When she’s inspired by a cool feature of language, she’ll blog it here.*