What is the difference between "on doing", "by doing", and "in doing"?
A difficult point to French learners of English as in all three cases, you would say "en faisant".
Example sentences, taken from the Longman Dictionary of Contemporary English:
What was your reaction on seeing him?
Howard had put his own life in danger in trying to protect the Queen.
She earns her living by selling insurance.
Best Answer
The difference between "on leaving" on the one hand and "by selling" and "in trying" on the other hand is easy: "on leaving" is to do with time and means "when you saw him", whereas "by selling" and "in trying" are to do with the cause and effect relationship. But there is a difference: by = she sells insurance in order to earn a living, it is her aim, it is a means to an end; in = Howard does not try to protect the Queen in order to put his own life in danger, it is just an occupational hazard for bodyguards, a side effect.