I've just come across these two phrases:

"A friend told me one day that he was..."

"A friend once told me that he was..."

What are the differences between those two phrases in terms of meaning? And which of them is preferable in terms of grammar and style?

closed as off-topic by Drew, user140086, Nathaniel, choster, Edwin Ashworth Dec 14 '15 at 8:09

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  • Welcome to EL&U. Questions that can be answered using commonly-available references are off-topic. I would advise you to take the tour and visit our help center to see how it works here. – user140086 Dec 13 '15 at 18:01

Rather than a question of connotation, it is more of a question of versatility. MLK's "I Have a Dream" speech includes this clause:

"I have a dream that my four little children will one day live in a nation where they will not be judged..."

Obviously, it would not work to say "my four little children will once live..." As far as meaning, the two phrases you have are identical. The difference between "once" and "one day" is that "one day" can express both past and future events while "once" can only express the former.

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