AN English teacher in Iran, Farhad H., recently sent me e-mail asking this very interesting question about preposition usage:
“I often have difficulty when it comes to the difference between the prepositions ‘in’ and ‘at.’ For example, which one of them is correct in this sentence: ‘Yesterday I saw many animals (in, at) the zoo’?”
My reply to Farhad H.:
Let me say at the outset that most preposition usage in English is essentially conventional, even quirkish in some cases, and a good number of the usages actually have no clear or evident logic of their own. Particularly in the case of the three most commonly used prepositions for establishing place and location, namely “in,” “on,” and “at,” it’s not easy to discern any logical difference between them. This is why many nonnative English speakers and learners of the language need to just patiently commit to memory the well-established ways of educated native English speakers in using prepositions.
We must be careful though that the prepositions we are memorizing are of the English standard used in the geographical location or region where we live, or of the English variety used by the target media for which we are writing or in which we are speaking.
The most widely used standards are, of course, the American English Standard and the British English Standard, and I am serving notice here that I can only present the general rules for preposition usage in the American English Standard. As they say, “Londoners live in a street and stay in farm cottages at weekends,” but “New Yorkers and English-speaking Manilans live on a street and stay in farm cottages on weekends.”
With that caveat about their applicability, here now are the rules for “in,” “at,” and “on” to indicate place and location:
The general rule: use “in” for an enclosed space, “at” for a point, and “on” for a surface.
The more specific guidelines are as follows:
Use “in” for spaces: “They always meet in a secret room [in a suburban hotel, in a parking lot, in a farm, in a ricefield].”
Use “in” for names of specific land areas: “She lives in a quiet town [in Tagaytay, in Cavite, in Southern Tagalog, in the island of Palawan, in the Philippines, in Southeast Asia].
Use “in” for bodies of water: “That kind of fish thrives in freshwater [in the river, in the lake, in streams, in the sea].”
Use “in” for lines: “The registrants are in a row [in a line, in a queue].”
Use “at” to indicate points: “You’ll find us at the entrance [at the taxi stand, at the supermarket, at the intersection].”
Use “at” for specific addresses, as in “She lives at 40 Lilac St.”
Use “on” for names of streets, roads, avenues, and boulevards: “Her apartment is on San Pablo Street [on Ortigas Avenue, on Santolan Road, on Roxas Boulevard].”
Use “on” for surfaces: “There’s a large stain on the floor [on the wall, on the ceiling, on the roof].”
Now, for indicating location with the prepositions “in,” “at,” and “on,” here are the general guidelines:
Use “in” in these cases: “The children are in the kitchen [in the garden, in the car, in the library, in the class, in school]. (The article “the” is mandatory except for the fourth and last examples.)
Use “on” in these particular cases: “They are on the plane [on the train, on the boat].”
Use “at” in these particular cases: “She was at home [at the library, at the office, at school, at work]when we arrived.”
At this point, following the drift of the above examples in the American English Standard, it should be clear by now that you should use “at” rather than “in” in the sentence you presented: “Yesterday I saw many animals at the zoo.”
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