を機に・を契機に: the difference
を機にN1
Meaning
Opportunity, Occasion
Past papers
Tested 3 times in past papers
Example
妻の妊娠を機にタバコを止めることにした。
I decided to quit smoking when my wife became pregnant.
を契機にN2
Meaning
Lead to, As a good opportunity to, As a result of, As a trigger
Past papers
Example
子供の独立を契機に家を改造することにした。
As a result of my children becoming independent, I decided to remodel the house.
How to tell them apart
「〜を機に」: elegant and written; treats the event as a great chance and the start of a new chapter.
「〜を契機に」: the most formal and official; common in political or economic commentary and big reforms, e.g. using a system reform as the turning point.
「〜をきっかけに」: from speech to general use; even a tiny everyday coincidence will do, e.g. starting Japanese after happening to watch an anime. Such small things don't suit the weighty 「を機に」.