Understanding "What", "Which", "Why", and "When" in English Grammar

In English, the interrogative words "what", "which", "why", and "when" are pivotal in formulating questions. Each serves a unique purpose, helping to extract specific types of information. Grasping their correct usage and differences is crucial for effective communication.

1. What are "What", "Which", "Why", and "When"?

  • What: Used to ask about things or activities.

    Example: What is your favorite book?

  • Which: Used to ask for a specific choice among a defined set of options.

    Example: Which dress do you prefer, the red or the blue one?

  • Why: Used to inquire about reasons or causes.

    Example: Why are you late?

  • When: Used to ask about time.

    Example: When is your birthday?

2. How to Use "What", "Which", "Why", and "When" in Sentences:

  • What: Use to inquire about objects, people, or actions. Example: What time is the meeting?

  • Which: Use when there are specific options or choices. Example: Which route should we take?

  • Why: Use to ask about reasons or justifications. Example: Why did she call you?

  • When: Use to ask about time-related queries. Example: When do you start your new job?

3. Avoiding Errors When Using "What", "Which", "Why", "When":

  • Ensure clarity about the type of information you seek. "What" and "which" can sometimes be interchangeable, but "which" is more specific.
  • Don't use "why" when asking about a person’s actions in a direct manner as it may sound accusatory.
  • Be specific with "when" to avoid vague responses.

4. The Difference Among "What", "Which", "Why", "When":

  • What vs. Which:

    • What is more general: What kind of music do you like?
    • Which is more specific: Which song from this album do you like the most?
  • Why vs. When:

    • Why asks for reasons: Why did the event get canceled?
    • When inquires about time: When was the event supposed to happen?

5. Cases When Not to Use "What", "Which", "Why", "When":

  • What and Which should not be used interchangeably when specificity is required.

    Incorrect (when options are clear): What option do you prefer, tea or coffee? Correct: Which option do you prefer, tea or coffee?

  • Avoid using Why in sensitive contexts where a less direct approach is better.

    Incorrect (may sound confrontational): Why did you do it? Correct (more tactful): What led you to make this decision?

  • When should not be used for non-time-related questions.

    Incorrect: When is your favorite color? Correct: What is your favorite color?


6. Practice What/Which/Why/When Exercises

What are the differences among "What/Which/Why/When" in English? This test was designed for you to practice "What/Which/Why/When". The test has 20 questions. Before taking the test, please read the following tips about "What/Which/Why/When".


- What: Used to ask for information, the thing

Ex: What are you doing?

- Which: Talk about a thing in things, or a person in a group

Ex: Which one do you want? Red car or blue car?

- Why: Ask reasons for something you use why

Ex: Why are you late?

- When: Ask about time, at what time

Ex: When will you come here?

 In conclusion, "what", "which", "why", and "when" are essential tools in the English language for asking a wide range of questions. Their correct application enriches conversation, aids in gathering precise information, and enhances clarity in communication.

Now You'll take a "What/Which/Why/When" test.

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