Tricky points of English ...

Explaining some of the everyday words in English, that are easy to confuse

Since and for

Since and for implying time or cause

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Terminology: "elapsed time" means a duration of time that has gone by.

"Since" often causes confusion, because it has two principal meanings: it can imply "elapsed time" (duration), or cause. Here are some examples:

A1 Since he arrived, everything has been different.
A2 Since it was Sunday, I stayed in bed longer.

In A1 since implies elapsed time, In A2 it implies cause:

The meaning of since - whether a conjunction , an adverb or a preposition - is determined by the structures and tenses used.

Four model examples to remember:

Duration - Since he won the lottery, he's become very lazy.
or Since winning the lottery, he's become very lazy.
Cause - Since he's the boss, we have to do what he says..
Duration - I've been here since yesterday, but John's been here for five days.
Duration - I came to London in 1990 and I've lived here ever since.

Explanations of these examples

Since used as a conjunction:

Model 1. Since normally implies duration (elapsed time) when the verb of the since clause is in a past tense and the verb of the main clause is also in the past. Since always implies duration if the verb in the since clause is a present participle..

Model 2. Since always implies cause when the verb of the main clause is in a present tense.

Since and for used as prepositions.

Model 3. Since is used to situate an event in relation to a moment in time (yesterday), but for is used to relate the event to a period of time or duration (five days). The verb in the main clause is normally in the present-perfect tense.

Since as an adverb.

Model 4 Since stands on its own, as in this common expression ever since: in this case it is a an adverb with the meaning "since then". Since as an adverb can never imply cause.

1. Since implying time or duration

When it implies time or duration, since is found either as a conjunction (introducing a clause) or as a preposition (introducing a phrase) , or occasionally as an adverb (standing alone).

1.1. If a "since" clause implies time, it must contain a verb in a past tense or an adverbial expression relating to the past.

B1    We haven't eaten anything since we got here.
B2    We haven't eaten anything since we've been here.
B3    I've been feeling sick since (last) Sunday .
B4 He left home last Sunday, and hasn't been seen since.

1.2. When the main verb in a sentence with a since clause (since you arrived) or a since phrase (since Tuesday) refers to a period of time including the present, a present perfect tense is necessary.

C1    See examples B1 - B3.
C2    I have been here since Tuesday.
C3    Since you arrived, he's been really happy.

1.3. If the whole sentence refers to past time, the main clause.will contain a verb in the past perfect tense. The since clause generally contains a verb in the simple past tense (preterite) or an adverbial referring to the past.

D1    We hadn't eaten anything since we arrived.
D2    I'd been feeling sick ever since I ate that cake.
D3    I hadn't eaten anything since six o'clock.

1.4. Since always implies time if (a) it is a preposition (examples C2, D3) or (b) it is followed by a present participle (as in. since going home).

Since or for ?

The essential rule. Used as a preposition (in front of a single word or a phrase) ,
since is required with a moment in time,
for is required when a duration, a period of time, or elapsed time is expressed.

A moment in time can be expressed either as an adverb (e.g. yesterday), an adverb phrase (e.g. last Tuesday, the start of term) or a verb of action (e.g. I ate...).

E1 - moment in time: . I've been here since last Tuesday.
E2 - elapsed time : I've been here for three hours.

The exception: used as a conjunction (in front of a clause containing a verb) since can be used with either a period of time or with a moment of time;

if elapsed time is implied (as in examples E3 and E4) , the verb in the since clause is normally in the present perfect.
If a moment of time is indicated (as in examples E5 and E6), the verb in the since clause is in the preterite

E3. I've felt much better since the window's been open
E4. He's lost weight since he's started running every day
E5. I've felt much better since I opened the window.
E6. He's lost weight since he stopped eating chocolate bars.

2. Since implying cause : present or past tenses are used

Since, implying cause, is a subordinating conjunction synonymous with as. There are two simple rules to remember

Rule 1. Since must imply cause, not time, when a since clause contains a present tense,

F1    Since it is raining, we are staying indoors.
F2    We will stay indoors since it is raining.
F3    Since he lives in Peru, he doesn't often visit us.

Rule 2. Since normally implies cause when the verb in the main clause and in the since clause are both in the preterite (simple past ) ,

G1 I ate all the chocolates since you left them behind.
G2 Since he was poor, he never took taxis.

To imply time, a present perfect would normally be used for the main verb

G11 I've eaten all the chocolates since I got home.

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