The time prepositions covered in this lesson — during, for, since, by, until, and within — are frequently confused with each other and with the simpler at/on/in group. They require careful attention to meaning, tense, and what kind of time expression follows. Several of these prepositions interact directly with the tense system: since almost always requires the present or past perfect, for can appear with multiple tenses, and by and until draw a clear contrast between deadline and continuation. Understanding these prepositions deeply allows teachers to explain tense-related errors that learners make around duration and time limits.
Before you start — think honestly about your own teaching and experience.
Look at the examples. Answer each question before reading the explanation — this is how your students will learn too.
Both sentences describe sleeping — but the time expressions after during and for are different types of information. What follows during? What follows for?
During is followed by a noun that names an event or period — the meeting, the lesson, the inspection, the holiday. It means at some point within that named event or throughout it. For is followed by a length of time expressed as a quantity — two hours, three weeks, a whole term. It answers the question how long? During answers the question when, in the context of which event? This is the key distinction: during + named event / for + length of time. A common learner error is during two hours — this attempts to combine during with a length of time, which is not how during works. Two hours is not the name of an event; it is a duration. For two hours is correct.
Since refers to a starting point. For refers to a duration. What grammatical difference do you notice between these two sentences and a simple past sentence like: The school opened in 1987?
Since and for, when used to describe a situation that started in the past and continues to the present, almost always appear with the present perfect tense (has been, have worked, have lived). Since is followed by a specific starting point in time: since 1987, since Monday, since I was a child. For is followed by a duration: for thirty-five years, for a long time, for several weeks. The simple past sentence (The school opened in 1987) describes a completed past event. The present perfect sentences (has been open since / for) describe a continuing situation. Learners who use simple past with since (I lived here since 2020) are making a tense error as well as a preposition confusion — understanding since and for requires understanding present perfect.
Only one of these sentences is natural English. Which one? And what is different about the meaning each preposition creates?
By Friday is the correct form for a deadline — submit it no later than Friday. The action must be completed before or at the time of Friday. Until Friday would mean keep submitting it continuously up to and including Friday — which makes no sense for a single action like submitting a report. By is used for deadlines: a single action must be completed no later than the stated time. Until is used for duration up to a point: she worked until Friday means she continued working and stopped on Friday. This is one of the clearest and most practical distinctions in this group: by = deadline (single completed action must happen before this point) / until = continuation (an ongoing action continues up to this point then stops). Many learners confuse these two because in some languages one word serves both purposes.'
| Form | Use / Meaning | Example |
|---|---|---|
| Preposition | Followed by | Example |
| during | Named event or period (a noun) | She fell asleep during the assembly. |
| for | Length of time (a duration) | She has been teaching for fifteen years. |
| since | Starting point in time; usually with present/past perfect | She has worked here since 2018. |
| by | Deadline — single action must be complete no later than this | Please submit the report by Monday. |
| until | Endpoint of a continuing action — action continues up to this point | The teacher worked until midnight. |
| within | Inside a time limit — completed before the limit expires | Please respond within three days. |
FOR WITH DIFFERENT TENSES
For is more flexible than since in terms of tense. It can appear with simple past for a completed duration: She taught there for ten years (and no longer does). With present perfect for an ongoing duration: She has taught here for ten years (and still does). With future for an anticipated duration: She will be away for a week. The tense choice signals whether the situation is ongoing or completed. A common error is using simple past + for when the situation is still ongoing — I lived here for five years (if you still live there) should be I have lived here for five years.
SINCE MEANING BECAUSE
Since also functions as a conjunction meaning because in formal and academic English: Since the school lacks resources, teachers must be creative. This is a different use from the preposition since (marking a starting point in time) and should not be confused with it. Learners at an advanced level may encounter both uses in formal texts.
BY VERSUS BEFORE
By and before are related but not identical. By Friday means no later than Friday — Friday itself is included. Before Friday means before Friday arrives — Friday itself is excluded. In practice this distinction matters for deadlines: submit by Friday means Friday is acceptable; submit before Friday means it must arrive Thursday at the latest. In everyday communication this distinction is often not critical, but in formal professional contexts it is worth knowing.
WHICH PREPOSITION DO I NEED? - Following a named event (the training, the holiday, the lesson)? → During. - Following a length of time (two hours, three weeks, a term)? → For. - Marking the starting point of an ongoing situation (with present/past perfect)? → Since. - Setting a deadline for a single completed action? → By. - Marking the endpoint of an ongoing, continuing action? → Until. - Stating a time limit within which something must happen? → Within.
Choose the correct preposition to complete each sentence.
Each sentence has one preposition of time error. Write the correct sentence and explain the mistake.
Use this sequence directly in class — guided discovery, no textbook needed. Tap each step to mark it done.
STEP 1 — DURING VERSUS FOR (7 minutes): Write two sentence frames on the board: She worked hard ______ (the training / three weeks). Ask learners to choose between during and for for each. Establish the pattern: during + named event / for + length of time. Ask learners to give five examples of named events (the lesson, the holiday, the inspection) and five durations (two hours, a week, a whole term). Then ask them to produce one sentence with each.
STEP 2 — SINCE: STARTING POINT AND TENSE (7 minutes): Write on the board: since 2019 / since Monday / since she arrived / since two years (this one is wrong). Ask learners: which one is incorrect? Why? Establish that since requires a specific starting point, not a duration. Then ask: what tense do we usually use with since? Draw out the present perfect connection. Ask learners to produce two since sentences using the present perfect.
STEP 3 — BY VERSUS UNTIL (8 minutes): Write the two sentences on the board: Submit by Friday / Submit until Friday. Ask learners: which is natural? What does each one mean? Act out the distinction: a single action (submit) with a deadline (by) versus a continuing action (wait, work, stay open) with an endpoint (until). Give five sentence frames and ask learners to choose by or until for each.
STEP 4 — WITHIN (5 minutes): Explain within as a formal alternative to by — inside a time limit, counting from now or from a reference point. Give three examples from formal school communications. Ask learners to produce one within sentence about their own school context (response time, results, repair schedule).
STEP 5 — FULL CORRECTION ROUND (8 minutes): Write five sentences containing errors from across the lesson. Ask learners to identify and correct each error and explain the rule they are applying. Use errors that reflect real learner confusions: during + duration, since + duration, until instead of by for a deadline.
Use directly in class — copy, adapt, or read aloud. No printing needed.
For each strategy, choose the option that best describes where you are now.
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