Learn Hardcore Japanese: henkou no riyuu wo mizikaku osiete kudasai. - Please briefly tell me the reason for the change.

へんこうのりゆうをみじかくおしえてください. Romaji: henkou no riyuu o mijikaku oshiete kudasai. Note: を is pronounced “o.” The long vowels in 変更 (henkou) and 理由 (riyuu) stretch the vowel sound.

What does the particle の do in 変更の理由?

It links two nouns to show a “of/for” relationship: 変更の理由 = “the reason for the change.” As a set phrase, you’ll also see the compound 変更理由 (no の), especially in forms or headings; it’s a bit more technical/compact, but the meaning is the same.

Why is it 理由を and not 理由は?

を marks 理由 as the direct object of 教える (“tell”). Using は would make 理由 the topic and slightly change the nuance:

理由を短く教えてください。 Neutral: “Please tell me the reason briefly.”
理由は短く教えてください。 “As for the reason, keep it brief” (often contrasting it with something else, like details to come later).

Why 短く and not 短い? What is 短く modifying?

短い is the adjective (“short”). To modify a verb, i-adjectives take the adverbial -く form: 短く = “briefly.” Here it modifies 教えて (“tell”), i.e., “tell [it] briefly,” not “a short reason.” If you really wanted to modify the noun, you’d say 短い理由, but for requests the adverbial “briefly” is more natural.

Would 簡単に, 簡潔に, or 手短に be better than 短く?

They each have a nuance:

短く: short in length/time; plain and common.
簡潔に: concise; crisp and to the point (good in writing/business).
簡単に: simply/briefly; can imply “in simple terms” (may sound like “don’t go into depth”).
手短に: briefly; “keep it short” (idiomatic). All are acceptable depending on tone: e.g., 変更の理由を簡潔に教えてください。 or 理由は手短にお願いします。

How polite is 教えてください? Are there softer or more formal options?

教えてください is standard polite and relatively direct. Softer/more formal options:

教えてもらえますか／教えてくれますか (softer ask: “Could you let me know?”)
教えていただけますか (more businesslike/humble toward the listener)
お教えいただけますか／お教えください (adds respect with お) Extremely formal but stiff: 教えてくださいませんか (rare in conversation).

Why is ください in hiragana, not 下さい?

When used as a request helper after a verb (…て), convention is to write it in hiragana: 教えてください. As a standalone “give me [thing],” you’ll also see hiragana today (e.g., 水をください). The kanji 下さい appears on some signs or older texts, but modern style generally prefers hiragana in requests.

Do I need to say “to me” (私に)?

No. It’s understood from context. The full pattern is “Person に Thing を教える,” so you could say 私に変更の理由を教えてください, but 私に is usually omitted when obvious.

Can I move 短く to a different position?

Yes, with small nuance changes. Natural options:

変更の理由を短く教えてください。 (default)
短く、変更の理由を教えてください。 (fronts the adverb for emphasis)
変更の理由は短く教えてください。 (topics “reason,” often contrasting) Avoid putting the adverb after ください. You can also pause-topic it: 変更の理由、短く教えてください。

Are spaces between words normal in Japanese?

No. They were added here for learners. Natural writing is: 変更の理由を短く教えてください。

Can I drop the object marker を?

In casual speech, particles sometimes drop, but with a polite request it’s better to keep を. A common alternative is to topic-mark with a pause/comma: 変更の理由、短く教えてください。 In writing, keep を.

Should I use 言う, 伝える, or 説明する instead of 教える?

教える: to teach/tell/inform (very common for “let me know”).
言う: to say. 理由を言ってください is grammatical but can sound blunt or like “state it.”
伝える: to convey (often to someone else). 理由を伝えてください = “Please pass on the reason.”
説明する: to explain. 理由を説明してください asks for an explanation (more detailed). For “tell me the reason,” 教える is the default.

Is 変更 the right word for “change”? How is it different from 変化, and is 理由 different from 原因?

変更: a deliberate/official change (settings, schedule, policy).
変化: a change in state/condition (often natural or observed).
変える/変わる: to change something / to change (intransitive).
理由: reason/motive/explanation (why someone decided something).
原因: cause (often of problems/phenomena). So 変更の理由 fits when asking why a plan or setting was changed.

Any other natural ways to say “Please keep it brief”?

Examples:

理由を短めにお願いします。
理由は手短にお願いします。
理由を簡潔にご説明ください。
理由のみお知らせください。 (if you want just the reason, nothing else)

Is ご教示ください acceptable in business emails? What about ご教授ください?

ご教示ください is good business Japanese for “please let me know/advise.”
ご教授ください literally asks for instruction in a skill/academic teaching; it’s often misused. For asking information or reasons, use ご教示ください (or ご教示いただけますと幸いです).

Why isn’t there a です/ます at the end?

The politeness is carried by ください. You don’t add です/ます after it. 教えてくださいです/ます is ungrammatical.