Character 亦

It marks the second member of a comparison or addition.

In Chinese, 亦 can also mean “again,” “merely,” or “although” in older or literary constructions; placement decides which reading fits. For plain modern “also,” 也 is the everyday alternative, while 亦 sounds chosen.

Any single-inventor story would overstate the evidence: in the surviving character record, the oldest layer shown is oracle-bone writing, followed by bronze, Chu-slip, and seal-script forms. Its traditional shape marks a person’s armpits, so its first job was anatomical. The later specialized form 腋 took over that sense.

why does 亦 feel formal?

Because it carries literary Chinese into ordinary writing.

If someone sends 亦 by itself in a Chinese message, read it as “also” or “too” before reaching for the historical armpit sense. Choosing 亦 over 也 can signal a formal, classical, or intentionally polished voice; use 也 when you want casual and unmarked.

The same character does not guarantee the same sound across Chinese and Japanese writing. Mandarin reads it yì, the sound spelled yi in pinyin; Japanese kanbun uses また (mata).