Both the usage of prepositions and articles are always the biggest headache for non-native English language learners—I think you’ll perhaps experience the same bewilderment when you first face complexity of the usage of prepositions called ‘te-ni-o-ha’ in Japanese language.
I was caught up with an primitive question, why it should be “earn a livelihood at one’s calling,” not “with/by one’s calling,” in the following sentence of the New Yorker’s (May 3rd) article titled “In Prague,” describing the hardship the thinking segment experienced under the Soviet-backed totalitarian Czech regime during 1970s.
Once they had been thrown out of the Writers’ Union, they were forbidden to publish or to teach or to travel or to drive a car or to earn a proper livelihood each at his or her own calling. For good measure, their children, the children of the thinking segment of the population, were forbidden to attend academic high schools.
As the text is from Philip Roth who received the Literary Service Award at the PEN Gala recently, it should be infallible.
But I as an English language novice tend to associate the preposition “at” with a speciffic working place rather than generic profession and job. Do we have to say “I earn my livelihood at my calling (writer’s/sales/guardsman’s job),” and no choice of other prepositions?