In sentence one the word since is a an

“Since” can be an expression of time, and it can mean “because”.

“Since” as a time expression

When used to express time, the word “since” means:
— from a time in the past until the present
— from a time in the past until another time in the past.

1. From a time in the past until the present

Because of its relationship with time “since” must be used with the correct verb tense. Have a look at these examples of a common mistake:

WRONG
He is out of the office since you last phoned.
As you may recall, the Paris office assists us with this project since it started.
Mr Jones is employed by the Company since September 2016.

In these three sentences the writers have made the mistake of using the Present Simple tense (is / assists / is employed) instead of the Present Perfect tense.

RIGHT
He has been out of the office since you last phoned.
As you may recall, the Paris office has assisted us with this project since it started.
Mr Jones has been employed by the Company since September 2016.

Note that these examples follow this pattern:
Present Perfect tense in the main clause and Past tense (or a date in the past) after “since”.

More examples:
No Public Authority or third party has raised any claims or allegations under Clause 4.1 since the Agreement was signed.

Since he joined the firm as a junior associate in 1998, he has become one of the most highly regarded lawyers in his field.

(Since joining… is an alternative structure that may be used in this type of sentence.)

In all sentences of this type you must use the Present Perfect tense in the main clause. However, the rule that you use the Past tense after “since” is flexible. Sometimes we can use the Present Perfect here as well. For example:

The department has been extremely busy since we have had an office in Mumbai.
I’ve been feeling much better since I’ve been taking more exercise.

We use the Past tense after “since” when we refer to a point in time in the past, and we use the Present Perfect after “since” when we refer to a period of time from the past until the present. We could rewrite the above two examples to refer to points in time (and use the Past tense after “since”) as follows:

The department has been extremely busy since we opened an office in Mumbai.
I’ve been feeling much better since I started taking more exercise.

2. From a time in the past until another time in the past

“Since” can also be used to express time from a starting point in the past until an end point in the past. Such sentences may follow this pattern:

Past Perfect tense in the main clause and Past tense after “since”.

We were sorry to lose MaxCo when they ceased operations in Poland in 2016. They had been a client of ours since they entered the country in 2003.

In 2013 I was asked to direct the company’s promotional film. I had not done anything like that since I worked in TV advertising in 1993.

When I arrived I realised that they had been in the meeting since 9 am.

It is also possible to use the pattern Past Perfect tense in the main clause and Past Perfect tense after “since”. For example:

It had been 20 years since I had directed any kind of film.

3. “Ever since”

You can add stress to “since” by adding “ever”.

Our two senior partners have known each other ever since they were at primary school.

He moved to London in 1994 and he has been living there ever since.

4. Do NOT use “since” to express present time, future time or general time

Note that in all the above examples, “since” is used to describe past time. When used to express time, “since” can ONLY be used in this way.

WRONG
Present
We want the office to start operating since now, or by the end of June at the latest.

Future
I’ll be in the bar since 7 o’clock this evening.

General time
The licence-granting procedure should not take longer than 90 days since the submission of the application.

Instead use “from”:

RIGHT
Present
We want the office to start operating from now, or by the end of June at the latest.

Future
I’ll be in the bar from 7 o’clock this evening.

General time
The licence-granting procedure should not take longer than 90 days from the submission of the application.

5. Do NOT use “since” to express duration

WRONG
The Landlord may terminate the Agreement with immediate effect if the Tenant is in arrears with payments since three months.

Although we would usually expect a decision within six weeks of making an application, the Claimant has now been waiting since ten weeks.

Instead use “for”:

RIGHT
The Landlord may terminate the Agreement with immediate effect if the Tenant is in arrears with payments for three months.

Although we would usually expect a decision within six weeks of making an application, the Claimant has now been waiting for ten weeks.

Another common mistake

WRONG
He worked at Microsoft since 2003 to 2006.

RIGHT
He worked at Microsoft from 2003 to 2006.

Do not use “since” with “to”. Use “from” and “to” or “from” and “until”. Another example:

He worked at the company from the moment he qualified until his retirement.

WRONG
According to the statement, no accidents at work or on the way to or from work have occurred since 2006 until now.

RIGHT
According to the statement, no accidents at work or on the way to or from work have occurred since 2006.

Because “since” — and the Present Perfect tense — incorporate “until now” into their meanings, including “until now” in the above sentence is not necessary.

“Since” meaning “because”

We do not recommend the course of action you propose since there is a risk that the employee will refer the matter to court.

This usage of “since” is rather formal, and may be ambiguous in some sentences because “since” is more commonly used to express time. Consider this example:

We have analysed the tax aspects of the transaction since we were instructed to do so.

This could mean “We have analysed the tax aspects because we were instructed to do so” or “We have been analysing the tax aspects from the time we were instructed to do so”.

As a result, I recommend using “because” or “as” instead of “since”.

When starting a sentence with the word «since», add a comma after the first clause (group of words containing a subject and a verb).

When starting a sentence with the word «since«, add a comma after the first clause (group of words containing a subject and a verb).

Since Mary is a doctor, she can prescribe drugs.

Since Mary is a doctor she can prescribe drugs.

We do not generally need a comma before «since» in mid-sentence.

I should skip dessert since I’m trying to lose weight.

I’ve been studying German since 2020.

Contents

• 1. How to Use Since in a Sentence
• 2. Commas in the Middle of a sentence
• 3. Starting a Sentence with ‘Since’
• 4. References

1. How to Use ‘Since’ in a Sentence

«Since» can be:

• A preposition to refer to a time in the past. Prepositions are followed by a noun or a pronoun (e.g., «I’ve been married since 2015.»)
• A subordinating conjunction to explain the reason for something (e.g., «My brother can achieve it since he has experience.»), or to indicate a period from a time in the past («I’ve been doing this since I arrived here.») Note that subordinating conjunctions, unlike prepositions, are followed by a subject and a verb.
• An adverb to mean «ago» or between then and now (e.g., «She went to the mall this morning, and I haven’t seen her since.»)

2. Commas in the Middle of a sentence

In the middle of a sentence, we do not commonly use a comma in front of «since«.

I’d like to travel to Japan since its culture is truly unique.

It’s been raining since yesterday.

Albert has lived in Rome since 2015.

Isabella has been looking for a job since she left school.

I wonder where my niece is. I haven’t seen her since Tuesday.

There are particular situations, however, where commas may be required. For example, use commas to set apart non-essential information.⁽¹⁾

Alice is planning to return to Madrid, maybe next month, since she has developed an emotional attachment to the Spanish culture.

I love her, despite our relationship stumbles, since she has been respectful and patient.

The Spanish government debt, already high since the financial crisis, exploded during the 2020 debacle.

3. Starting a Sentence with ‘Since’

As mentioned before, we can use «since» to introduce a group of words containing a subject and a verb (clause).

Since my sister is an excellent cook, she prepared a delicious meal.

In this situation, if the clause introduced by «since» comes at the beginning of a sentence, we must add a comma after the first clause.

Since I want to learn a new language, I registered for a Chinese course.

Since I want to learn a new language I registered for a Chinese course.

More examples:

Since they’re going to arrive next week, we have plenty of time to prepare for the meeting.

Since copper is still the material of choice for electric power, the demand of copper is growing by leaps and bounds.

Since the current situation seems a perfect setup for yield curve control, the European Central Bank will probably implement this policy next year.

Instead of introducing a clause, you can use «since» to introduce a noun phrase. Phrases, unlike clauses, do not contain a subject and a verb.

Since 1980 the US GDP has been declining.

The comma after short introductory phrases like these can be easily omitted if the sentence is clear.⁽²⁾

Since then I have been learning marketing.

Since 2018 Rebecca has been working here.

4. References

(1) Strunk JR., William; White, E.B. The Elements of Style. Chapter 1 — Elementary Rules of Usage.

(2) Kaufman, Lester; Straus, Jane. The Blue Book of Grammar and Punctuation. Chapter 2 (punctuation).

Since can be used as an adverb, a conjunction and a preposition.

Since as a preposition

As a preposition, since is followed by a noun/noun equivalent which acts as its object.

• She has changed a lot since her marriage.
• Everything has changed so much since our last meeting.

As an adverb

When since is used as an adverb, it is not followed by a noun.

• The boy went missing on Tuesday and hasn’t been seen since.

As a conjunction

Since can also be used as a conjunction. As a conjunction, since is used to connect two clauses. Clauses introduced by since typically show one of the two associations: time or cause/reason

• Since he had not studied hard, he failed his exam.
• Since I had no money, I couldn’t buy anything to eat.
• Since she was tired, she took some rest.

A since-clause introducing reason usually comes at the beginning of the sentence. A since-clause indicating time can come either before or after the main clause.

• She has written many books since she left college. / Since she left college, she has written many books.

Notes

When since is used to talk about time, the verb in the main clause is usually in the present perfect or past perfect (simple or continuous) tense.

• She had been acting in films since she was four.
• I have been working on this project since the end of June.
• It has been raining since morning.

Sometimes the simple present or simple past tense is also used.

Since means ‘starting at a particular point in the past and continuing until now’.

• I have known him since he was born.
• India has been an independent country since 1947.
• It has been several decades since India won a gold medal in Olympic Hockey.
• It has been several centuries since Vasco da Gama landed in India.

Ever since

• She started teaching at twenty and has been doing it ever since.
• Ever since I was a child, I have wanted to become a writer.

The word ‘since’ can act as a preposition or a conjunction (also an adverb). In your sentence:

«She had told him she wanted a divorce two days ago, and neither of them had slept since.»

‘Since’ is simply a preposition, linking the dependent clause:

«… , and neither of them had slept since.»

back to the independent clause you started the sentence with:

«She had told him she wanted a divorce two days ago …»

Maybe you are more familiar with ‘since’ as a conjunction? In which case the sentence would have read:

«Neither of them had slept since [conjunction] she had told him she wanted a divorce two days ago.»

Note: Ignore any silly rule you may have heard that tells you not to end sentences with prepositions. It’s bunkum.