Why these contractions exist
Casual, frequently used grammatical combinations naturally compress over time in spoken language, and that compression eventually crosses over into everyday written Korean as well. It's a similar underlying phenomenon to English contractions like "don't" or "isn't," though the specific mechanics — vowel contraction rather than dropped letters — work differently.
Formal writing vs. casual writing
Contracted forms like 돼, 해, 예요, 그건, and 뭘 are broadly acceptable in casual and even much semi-formal writing, since they're standard contractions rather than slang. Very formal or academic documents, however, sometimes lean toward spelling out the fuller original form for a slightly more formal register.
Frequently Asked Questions
How do I know whether to write 되 or 돼?
Try substituting the full form 되어 into the sentence in place of the contraction — if it still reads naturally, 돼 is correct there; if it doesn't, 되 paired with a different ending is what the sentence actually needs.
Are contractions like these okay to use in formal writing?
Most are fine even in fairly formal contexts, since they're standard accepted contractions rather than slang — but very formal or academic writing sometimes prefers spelling out the fuller original form instead.