质疑 means 'to question' or 'to challenge'—especially in a critical, thoughtful, or skeptical way. The character 质 (zhì) originally meant 'to interrogate' or 'to examine closely', while 疑 (yí) means 'to doubt' or 'to suspect'. Together, they form a verb emphasizing active, reasoned doubt—not mere uncertainty, but an intentional act of seeking clarification or challenging assumptions. It is commonly used in academic, journalistic, legal, and public discourse contexts, often implying intellectual rigor or moral responsibility.

This word carries a neutral-to-formal register and is rarely used in casual daily conversation. It frequently appears with objects like authority, claims, methods, evidence, or official statements. While it can imply disagreement, it does not inherently mean 'to oppose'; rather, it signals a demand for justification or transparency. It is often followed by a clause introduced by '的' or a noun phrase indicating what is being questioned (e.g., 质疑他的结论, 质疑这项政策).