What Is Their Main Difference?
Parts of Speech
'When' and 'once' have different functions in the English language. We have summarized their parts of speech in the table below for better understanding:
If you pay attention to the table illustrated below, you can see that 'when' and 'once' can be used as conjunctions. Conjunctions are categorized into different groups. 'When' and 'once' are categorized as subordinating conjunctions.
Talking about Time
'When' and 'once' both express time. They are used to show that something happens as soon as something else occurs.
I was sleeping
I will come back
Are They Interchangeable?
As conjunctions 'when' and 'once' express the same meaning= 'as soon as,' and 'after.' Note that 'once' is more emphatic than 'when.'
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