FOR, SINCE or AGO? Prepositions of Time - English Grammar

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Hi everybody, my name is Alisha, and today I'm going to talk about the difference between

“for” and “since.”

I'm also going to talk about how to use “ago,” so let's get started.

Okay, the first thing I want to talk about is the word “for.”

We use the word “for” before a period of time, so before a period of time can mean

minutes, it can mean years, it can mean days, seconds, hours; a period of time or a length

of time.

We use the word “for” before that phrase to talk about the length of time that something

happens.

So for example, for ten minutes, we use it before ten minutes.

For five years, five years as a length of time.

For a day, a day is also a length of time.

For a lifetime, one whole lifetime, a person's whole lifetime can be a period of time, we

use "for" before in this case.

There's also "for" an eternity; an eternity, we can use this to mean a very very long time,

it's sort of an exaggerated phrase but for an eternity means a very very long time.

These are all lengths of time and we should use the word "for" before we want to express

them.

Okay, so let's talk about something a little bit different then, the word "since."

"Since" is used before a specific point in the past, we often use since with present

perfect tense, maybe you've seen another video that we did about the present perfect tense

and how to make present perfect tense sentences.

We often use "since" in present perfect tense sentences.

"For" is also used in present perfect tense sentences but the two are used a little bit

differently.

"Since" is used to talk about a specific point in the past, a specific point in the past,

maybe, where something happened or something began.

So, for example, since last night.

This shows us that since last night, last night something happened or something started,

and it's continuing.

So "since" shows us that something has been continuing or the effect has been continuing

"since" a point in the past; it began at a point in the past and continues or the effect

continues until the present, "since," tells us all this information.

Another example, since 2014.

So this is the point in time, 2014 is the year at which something changed or an action

started, or the effect of an action began.

So we can use "since" in this case.

Another point in time can be a season, like, winter.

Since winter, since summer, since autumn.

We can use "since" before a season, we also have points in time in the day, since this

morning, since this evening, since last night, was my first example here.

We can also use morning, this morning, this morning, today, as a point in time.

Finally, I have one more example, since last week.

So points in time, there are a lot of different points in time but just be careful, length

of time uses "for," point in time uses "since," and "since" shows us that there's some action

that's continuing or the effect of some action continues until the present.

So please be careful.

Period of time, point in time; "for" and "since."

Okay, so the next point that I want to talk about is "ago."

There are a couple of different ways that we can use "ago," and the first one I want

to talk about is one we use for past tense statements or past tense situations.

So we use "ago" to talk about points in time where actions or changes occurred.

So, for example, three years ago I got a new job, or five minutes ago I ate lunch, or,

two days ago I saw my friend, or two jobs ago I didn't have much experience.

So all of these statements are used to talk about a past tense point in time where something

changed or some action occurred, so we use "ago" in this way with the past tense to mark

a change or something happening.

So there's a second use of "ago" that I want to talk about.

We can use "ago" with "since" and a time period, this is something we often use in present

perfect tense statements, like we talked about here, with "since."

What I mean by that, for example, is "since" + time period + "ago."

So for example, since three years ago, or since five minutes ago, or since two months

ago.

So here you'll see we're using a time period, I know I said to use time periods with "for,"

but this can be kind of a useful pattern because if you use the word since on accident but

you want to express a time period instead, you can save yourself by adding "ago" to the

end of it.

So if you're working on making a sentence, for example, and you're speaking and you accidentally

use the word "since," even though you know you want to use a time period, save yourself

by attaching "ago" to the end.

So since three years ago, something has occurred, something has been continuing.

So because "since" is here it shows us, like we talked about with "since" here, the action

or some effect of that action is continuing from this point in time, so we can use this

pattern as well, "since," time period, "ago".

Okay, so this is a lot of information, let's try to make a few sentences, I've prepared

a few example sentences, so let's take a look.

Alright, the first one.

We've lived here _______ three years.

So how do we know which to use?

First, we see "we've," we have, we have lived here, this is a present perfect tense sentence,

we've lived here plus three years.

So I see a time period here, that means I should use "for," because we need to use "for"

before periods of time.

So, we've lived here for three years is the correct sentence.

Good.

Okay, let's look at the next one then.

They've been studying _______ 2014.

So here, I see a point in time, a point in time, a specific point in time, and another

really good hint is the grammar here, I see the present perfect progressive or the present

perfect continuous tense here, "they've," meaning they have, plus "been studying," this

shows a continuing action.

So all of these give me hints about which one I should use.

They've been studying since 2014 is the correct answer here.

Next one.

He left the office five minutes ______.

Okay, here we see this is a past tense statement, he left, so "left" is the past tense form

of the verb "to leave," so we see here a period of time, five minutes, yes, but after five

minutes is our space, meaning we need to use "ago."

Five minutes ago.

We always use "ago" after the period of time.

Okay, next one.

I've been reading this book _______ last week.

So again, we see this "been reading," this present perfect continuous tense shows us

an action has been continuing, this shows a continuing action or a continuing effect.

So we know we should use "since."

I've been reading this book since last week.

So, last week, as we talked about here, is our specific point in time.

Let's take a look at the next example sentence, it's a little bit tricky, it's a little bit

difficult.

Here, we see the same "been waiting," the same present perfect continuous or present

perfect progressive tense, this shows us that an action has been continuing, yes, but I've

used the word "ages" here, so "ages" is sort of a casual expression which means a very

long time, that means it's a time period, this is not a specific point in time; ages

is not a specific point in time, it's actually a time period.

So we should use "for" here.

You've been waiting here for ages, for a long time, is what this sentence means.

Okay, last one.

They've been dating ______ about two weeks ______.

Okay, so here there are two spaces where we can use a word, that should probably give

you a good hint, it'll be this "since" and "ago," but let's talk about why.

Here, again, we have this continuous form, they've been dating, "dating" as the continuous

or the progressive form of the verb "to date."

So we have "about" plus "two weeks," so there's a period of time there, yeah?

In this case then, we should use since about two weeks ago.

So two weeks ago they started dating, or they've been dating since about two weeks ago, we

can use both of these sentences to express the amount of time they have been dating.

Okay, so those are a few points about when to use “for,” “since,” and “ago.”

We also talked about some grammar points that you can use these words with.

If you have any questions about those, check out some of the other videos we've made on

this channel, especially about the present perfect tense.

They can help give you some more background about those grammar points.

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