由・よし

• Reading: よし
• Romaji: yoshi
• Formation: Verb plain form + 由 / ～とのよし / ～た由
• Kanji breakdown: 由 (よし): reason, cause; by extension, reported information

Meaning

A dependent noun meaning 'it is reported that' or 'I have learned that,' used to mark the content of information the writer has received from another source. It conveys hearsay in formal written communication.

よし (written 由 in kanji) is a formal hearsay marker used predominantly in written Japanese, especially in business letters, official correspondence, and formal announcements. It attaches to a preceding clause (often in plain form or polite form) and signals that the writer is relaying information received from someone else. Common patterns include ～とのよし (I understand that), ～た由 (I have heard that), and ～の由 (it is reported that). Unlike そうだ (hearsay) or ということだ, which are appropriate across registers, 由 is reserved for formal written contexts and lends a distinguished, epistolary quality. It is rarely used in spoken Japanese.

Examples

1. 先方から契約の見直しを希望している由、ご連絡がありました。 We received word that the other party wishes to review the contract.
2. 部長がご出張中の由、改めてお伺いいたします。 I understand the department head is away on a business trip; I will call again.
3. 新工場の建設が順調に進んでいる由、安堵いたしました。 I was relieved to hear that the construction of the new factory is progressing smoothly.

Usage Guide

Context: written, business, correspondence

Tone: reportorial

Do Say

• ご退院なさった由、心よりお喜び申し上げます。
• 新任の部長がご着任された由、ご挨拶に伺いたく存じます。
• プロジェクトが無事完了した由、お疲れ様でございました。

Don't Say

• 田中さんが来た由。(Using 由 in casual spoken context — it is restricted to formal written Japanese) → 田中さんが来たそうです。
• 明日は雨の由です。(Using 由 for a weather forecast — it is for relaying information received from a person, not impersonal sources) → 明日は雨だそうです。

Origin & History

由 (よし) originally meant 'reason,' 'cause,' or 'means' in classical Japanese. Through its use in reporting the reasons and circumstances behind events, it came to function as a formal hearsay noun, especially in epistolary Japanese from the medieval period onward.

Cultural Context

Generation: All ages

Social background: Universal