Western Comparison: “Doctor” vs. “Dàifu”: In English, “Doctor” is the standard term. A term like “Physician” is slightly more formal, and “Doc” is informal.
大夫 (dàifu) doesn't map perfectly. It's more colloquial than
医生 (yīshēng) but also carries more historical weight and respect when used in direct address. The best way to understand it is to see
医生 (yīshēng) as the neutral, modern, and universal job title (“He is a doctor”), while
大夫 (dàifu) is a traditional and common term of address (“Hello, Doctor”).