'What do' and 'what does' are two phrases that often puzzle English learners, yet they serve distinct purposes based on the subject of a sentence. The key difference lies in their grammatical usage related to person and number.
When you ask a question using 'what do,' you're typically addressing someone directly or referring to multiple subjects. For instance, if you want to know about someone's routine, you'd say, "What do you usually eat for breakfast?" Here, 'you' is second-person singular. Similarly, when asking about a group like students or friends—"What do they enjoy doing on weekends?"—the plural form necessitates the use of 'do.'
On the other hand, 'what does' comes into play when your subject is third-person singular: he, she, it—or any single noun like ‘the cat’ or ‘my brother.’ A typical example would be asking about someone's job: "What does your sister do for work?" In this case, since we're talking about one individual (your sister), we correctly pair it with ‘does.’
It's also important to note that while both phrases inquire about actions or habits—the former being more general ('do') and applicable across various subjects—the latter focuses specifically on singular entities ('does'). This distinction can sometimes lead to confusion; for example:
- Incorrect: "What do your sister study?"
- Correct: "What does your sister study?"
Additionally, there are nuances in context where these phrases shine. When discussing habitual actions versus specific inquiries into capabilities or functions—like machines—you might say:
- “What does this machine do?” (focusing on its function)
- “What do people generally think of new technology?” (a broader inquiry).
Grasping these subtleties not only helps avoid common mistakes but enriches conversational skills as well. So next time you're curious about what someone engages in daily or professionally remember: if it's I/we/you/they—use ‘do’; if it’s he/she/it—a simple switch brings us back to ‘does.’