"I've been waiting since three hours." Painful but extremely common. So is "during I was eating, the phone rang." Both sentences use a time word that sounds fine in your head but lands wrong on a native speaker's ear. The fix is small. Let's clean it up.

Quick Answer

• Since = a starting point in the past. (since Monday, since 2019)
• For = a length of time. (for two hours, for three years)
• During = inside an event or a noun phrase. (during the meeting, during summer)
• While = inside a clause with a verb. (while I was eating)

If the next word is a point in time -> since. If it's a number + unit -> for. If it's a noun describing an event or period -> during. If it's a full mini-sentence with a subject and verb -> while.

The Simple Rule

• Since + starting point: tells you when something began. Almost always with present perfect or past perfect tenses. "I've worked here since January."
• For + duration: tells you how long something lasts. Works in nearly any tense. "I worked there for five years."
• During + noun phrase: tells you inside what period or event. "I fell asleep during the movie."
• While + subject + verb: tells you at the same time as another action. "I fell asleep while the movie was playing."

The last two are siblings, not twins. During is followed by a thing (an event, a period). While is followed by a sentence (something with its own subject and verb). Many learners try to swap them, and that's the single biggest leak point in this whole family.

Natural Examples

Starting point — since

• I've lived in Taipei since 2018.
• She hasn't called since Monday.
• We've been friends since elementary school.

Length of time — for

• I lived in Taipei for five years.
• She talked for an hour without stopping.
• We've known each other for ages.

Inside an event or period — during

• My phone rang three times during the meeting.
• He traveled a lot during the summer.
• Nobody moved during the earthquake.

At the same time as another action — while

• My phone rang while I was presenting.
• He read three novels while he was on vacation.
• Nobody moved while the building was shaking.

Notice how cleanly the during / while pair lines up if you keep the meaning the same and just change what comes after. During the meeting = a noun. While I was presenting = a clause. Same idea, two different grammar slots.

Common Mistakes

• "I've been waiting since three hours." → "I've been waiting for three hours." · Three hours is a length, not a starting point.
• "I lived in Korea since five years." → "I lived in Korea for five years." or "I've lived in Korea since 2020." · Since needs a point in time, not a duration.
• "During I worked there, I met my best friend." → "While I worked there, I met my best friend." · During can't be followed by a clause.
• "While the meeting, my phone rang." → "During the meeting, my phone rang." · While can't be followed by just a noun.
• "He stayed for since Monday." → "He has stayed since Monday." or "He stayed for three days." · Pick one — since or for, never both.

A subtle tense detail: since almost always pulls a perfect tense ("I have lived... since..."), because you're describing a stretch that began in the past and continues into now. For is more flexible — it works in simple past ("I lived there for five years, then moved"), present perfect ("I've lived here for five years"), and future ("I'll be there for two weeks"). If your sentence uses since with a simple past verb, double-check; it usually wants present perfect.

Exam Trap

Reading and listening sections lean on this family because the words look interchangeable to learners but lock down exact meanings to natives. TOEIC and IELTS both like sentences like: "The number of applicants has tripled ___ the new policy took effect." If you reach for during, you'll lose the point — "the new policy took effect" is a full clause, so the slot needs either since (treating it as a starting moment) or after. TOEFL Listening often hides this in narrative recounts where the speaker switches between "during my internship..." and "while I was interning..." in the same paragraph. The two phrases describe the same period, but one is followed by a noun and the other by a clause — and a comprehension question may quietly check whether you can paraphrase one as the other.

Mini Practice

1. I've been studying Japanese _____ I was twelve.
2. She lived in Berlin _____ almost a decade.
3. Please turn off your phone _____ the performance.
4. My laptop crashed _____ I was saving the file.
5. We haven't seen each other _____ the last conference.

Answer Key

1. since — "I was twelve" is a starting point in the past.
2. for — "Almost a decade" is a duration.
3. during — "The performance" is an event (a noun phrase).
4. while — "I was saving the file" is a clause with its own subject and verb.
5. since — "The last conference" is a specific past point.

Tiny Summary

Ask yourself one question: what kind of thing is the next word? A point in time, a duration, an event, or a full mini-sentence? Match it, and your time words will stop leaking.