Relative Adverb: When for Time

Imagine you are telling a friend about a great party. You have a noun like the moment or the year. You want to add more detail to that noun. Instead of starting a new sentence, you use when. This word starts a relative clause. This clause acts like a big adjective. It describes the time you just mentioned. It tells us exactly which day or hour you mean. It is like adding a filter to a photo. It gives the listener more context. You are essentially saying, "Here is a time, and here is what happened then."

1. 1Building these sentences follows a simple recipe. Follow these steps to get it right every time:
2. 2Start with a time noun (e.g., the day, the summer, the hour).
3. 3Add the relative adverb when immediately after the noun.
4. 4Follow up with a subject and a verb (a full clause).
5. 5Finish the rest of your thought.
6. 6Example: I'll never forget the day (Time Noun) + when + we first met (Clause).
7. 7It is like building a sandwich. The time noun is the bottom bread. When is the spread. The clause is the filling. Simple, right? Even native speakers sometimes skip when in casual speech, but using it makes you sound clear and polished.

Use when whenever you want to define a specific period. This could be a broad era like the 90s. It could be a specific moment like the second. It is perfect for storytelling. Use it in job interviews to describe a time when you solved a problem. Use it when ordering food to describe the time when you had that amazing pizza. It works for past, present, and future.

• "1998 was the year when I graduated."
• "Monday is the day when I am busiest."
• "I look forward to the day when we can travel again."

You cannot use when if the noun isn't about time. That sounds obvious, but people try it! Also, don't use when if you are using a preposition like in or on at the end.

• ✗ "That is the house when I lived."
• ✓ "That is the house where I lived."
• ✗ "The day when I was born on..."
• ✓ "The day when I was born..."

If you use which, you usually need a preposition. If you use when, you don't. Think of when as a package deal. It includes the meaning of "at that time" or "on that day." Adding extra prepositions is like wearing two hats. One is enough!

A very common slip-up is using which instead of when. Remember, which describes things, but when describes times.

• ✗ "I remember the summer which we went to Italy."
• ✓ "I remember the summer when we went to Italy."

Another mistake is repeating the time word.

• ✗ "The hour when the bell rings at that hour is noon."
• ✓ "The hour when the bell rings is noon."

Don't be afraid! Even if you mess up, people will usually understand you. Just think of it as a grammar traffic light. When means "go ahead and describe the time."

You might see in which or on which in formal books. These are the fancy cousins of when.

• Formal: "The year in which the war ended..."
• Natural: "The year when the war ended..."

In casual chat, you can even use that or nothing at all.

• "The day that we met..."
• "The day we met..."

However, for your B1 exams and clear communication, when is your best friend. It is specific and always correct for time. It is like choosing the right tool for the job. You wouldn't use a hammer to eat soup, right?