I really can't figure out where the masu form comes from. I thought it might be from kobun volitional む + causative す but that's -(a)ます not -(i)ます.

Both conjugations of ません and ましょう are identical to how the Kyoto dialect conjugates す. That's as much as I could figure out, I'm really stumped here.

  • Answered here in a separate question about ~ません: Origin of ません (-masen)?. If you can read Japanese, there's a fuller description available in the Kotobank's mirror of Shogakukan's [国語大辞典]{こくごだいじてん} dictionary here. May 20, 2021 at 17:13

1 Answer 1


According to Frellesvig (A History of the Japanese Language, p338), the masu auxiliary is derived from the polite auxiliary marase, which apparently is a humble word for 'give'. The marase form emerged in Late Middle Japanese (1200-1600) and is itself a causative form derived from the earlier mawir ('come').

Beyond that, I don't know anything, but I suppose you can imagine the concept of 'giving' being applied to one's own actions to suggest a humbleness/politeness in a similar way that the current ~てあげる is used.

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