いかんによって

1. Usage and Register
いかんによって is used in official documents, legal contexts, or formal business reports. In official government and legal documents, it must be written in hiragana（いかんで, いかんによって）according to drafting guidelines. The kanji form（如何で, 如何によって）appears in standard formal writing and novels, but modern corporate style guides often default to hiragana, as 'いかん' is an ateji/jukujikun reading not listed in the official Joyo Kanji table. It is rarely used in spoken Japanese unless the situation is extremely stiff or professional. It suggests that there are multiple possible outcomes depending on the circumstances. The forms いかんで and いかんでは are considered the standard and most frequent variations of this pattern.

2. Sentence-Ending Form
In formal reports or declarations, you may see the sentence-ending form 〜いかんだ. This directly states that the outcome is contingent upon the preceding noun (e.g., 「すべては君の努力いかんだ」 - Everything depends on your effort).

3. The Particle は (いかんによっては)
The addition of the particle は highlights one specific potential outcome out of a range of possibilities. This outcome can be either positive or negative (e.g., 「成績のいかんによっては、奨学金がもらえる」 - Depending on the grades, you might receive a scholarship). It is often paired with expressions of possibility at the end of the sentence.

4. Formation

• Noun + (の) + いかんによって / いかんで

Crucially, the preceding noun must inherently contain a range of possibilities, degrees, or variations（幅のある言葉）, such as 成績（せいせき - grades）, 結果（けっか - results）, 態度（たいど - attitude）, 状況（じょうきょう - situation）, or 理由（りゆう - reason）. It cannot be used with static nouns. The particle の is optional and can be used or omitted freely with both verbal nouns and non-verbal nouns (e.g., 「理由いかん」 or 「理由のいかん」, 「検査いかん」 or 「検査のいかん」).

5. Nuance vs. Similar Patterns
The most direct, less formal equivalent to this pattern is 〜次第で or 〜次第だ, which is universally taught as the standard counterpart to いかんで. Furthermore, unlike the simple によって, which just means 'depending on', いかんによって focuses on the state, outcome, or nature of the noun (i.e., 'how the noun turns out' or 'what the noun is'). For example, 「理由いかん」 (what the reason is) or 「検査の結果いかん」 (how the test results turn out).

6. Trailing Clauses
The standard forms いかんで and いかんによって are typically followed by verbs of change or decision, such as 決まる（きまる）, 変わる（かわる）, or 異なる（ことなる）. In contrast, the forms with は (いかんでは / いかんによっては) are usually followed by expressions of possibility, such as かもしれない or 可能性がある（かのうせいがある）.

7. 'Regardless of' Counterparts
It is important to note the negative or independent counterparts to this pattern, which mean 'regardless of'. These include 〜いかんにかかわらず, 〜いかんによらず, and 〜いかんを問わず. For example: 「理由いかんにかかわらず、遅刻は認めない」（りゆういかんにかかわらず、ちこくはみとめない - Regardless of the reason, tardiness will not be accepted）.

8. Noun Modification
When modifying another noun, the form 〜いかんによる is used. This directly connects the dependency to the following noun. For example, 「努力いかんによる成功」（どりょくいかんによるせいこう - success that depends on effort）.