何以 / 何在: why / where is… (classical interrogatives)
语体 / register & style
Tone colorsā tone 1á tone 2ǎ tone 3à tone 4a neutral
S + 何以 + V ？ | N + 何在 ？
Classical 何 ("what, which") survives in written interrogatives often used in titles or rhetorical questions:
• 何以 = "why, how is it that" (= 为什么/凭什么): 何以见得？(what makes you say so?).
• 何在 = "where is, what does… consist of" (= 在哪里): 意义何在？(what's the point?), 原因何在？
Also: 何时 (when), 何处 (where), 何为 (what is). They give a reflective, argumentative tone.
Examples
如果机器能写诗，人类创作的意义何在？
Rúguǒ jīqì néng xiě shī, rénlèi chuàngzuò de yìyì hézài?If a machine can write poetry, what's the point of human creativity?
他何以如此自信？
Tā héyǐ rúcǐ zìxìn?Why is he so confident?
你说这个方法不行，何以见得？
Nǐ shuō zhège fāngfǎ bù xíng, héyǐ jiàn dé?You say this method won't work: what makes you think so?
Common mistakes
✗ 何在 at the start: ✗ 何在意义？ → ✓ 意义何在？ (何在 goes last).
✗ 何以 in everyday speech: ✓ 为什么.