べし

Should/must (Classical)

Level 6Sounds Like beshi

べし is a classical Japanese auxiliary that functions as a 'multi-modal' marker. While its modern descendant べき primarily means 'should,' the original べし covers a wider range of meanings including strong conjecture (must be), volition (shall), potential (can), and commands (shall/must).

How It Works

べし is one of the most important auxiliaries in classical Japanese (文語（ぶんご）) and remains highly visible in modern formal contexts through its various inflections.

1. Attachment Rules:
べし attaches to the 終止形（しゅうしけい） (Terminal Form) of verbs. However, there is a major exception: for ラ変（らへん） (r-irregular) verbs like ある and verbs ending in the suffix -り, it attaches to the 連体形（れんたいけい） (Attributive Form). For example, it is あるべし, not ありべし. For the verb する, the classical terminal form is すべし, while the attributive form is すべき. In modern Japanese, すべき and するべき are both commonly used.

2. Modern Descendants:
While you rarely hear the terminal form べし in daily speech, its inflections are everywhere:

  • べき (Attributive): The standard modern way to say 'should.'
  • べく (Continuative): Used in formal writing to mean 'in order to' (e.g., 成功すべく — in order to succeed).
  • べからず (Negative Command): Seen on signs meaning 'Must not' (e.g., 入るべからず — Do not enter).

3. Nuance:
Unlike はず, which is based on logical expectation, or ものだ, which describes general social truths, べし implies a natural or objective necessity. It suggests that the outcome is dictated by the social order or the laws of the universe.

Examples (4)

  1. 若者は大いに学ぶべし。

    Young people ought to study hard.

    Word by Word: Young people (topic) greatly study should.

    This uses the 'Obligation' sense of べし. It sounds formal and exhortatory, like a proverb or a formal speech.

  2. この計画は必ず成功すべし。

    This plan shall surely succeed.

    Word by Word: This plan (topic) certainly success do-should.

    Here, べし expresses 'Strong Conjecture' or certainty. Note the use of すべし (the classical terminal form of 'to do') instead of the modern するべき.

  3. 芝生に入るべからず。

    Do not enter the grass.

    Word by Word: Lawn into enter must-not.

    This uses the negative inflection べからず to issue a formal prohibition, commonly seen on public signs.

  4. 疑うべくもない事実だ。

    It is a fact that cannot be doubted.

    Word by Word: Doubt-potential-not-even fact is.

    This uses the potential sense of べし in its continuative form べく, combined with もない to mean 'no possibility of.'

Common Mistakes

  • Using べし for casual advice to friends.

    このケーキを食べるべし！
    このケーキ、食べてみて！

    べし (and its modern form べき) carries a heavy sense of moral or objective duty. Using it for light suggestions like trying food sounds overly bossy, aggressive, or like you are roleplaying a medieval warrior.

  • Confusing べし with はず for logical predictions.

    電車は五時に来るべし。
    電車は五時に来るはずだ。

    はず is used for logical expectations based on facts (like a schedule). べし implies the train has a moral obligation or a cosmic necessity to arrive, which is unnatural for simple facts.

How It Connects

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べしLevel 6Should/must (Classical)

Learn This First

べし is a classical Japanese auxiliary verb that expresses obligation, potential, or expectation. To understand it, learners should first be familiar with its modern equivalent '〜べき'. Additionally, since it functions as a verb ending, a solid grasp of basic verb concepts and sentence structure is required to see how it modifies the action of the sentence.

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べし