We have been traveling around the United States
We have been traveling around the United States for one month.
She hasn't taken a vacation
She hasn't taken a vacation for a long time.
SINCE when? FOR how long?
If you don't know whether to use for or since, ask yourself...
for HOW LONG?
...a thousand years
...a long time
...the rest of my life
...a couple weeks
For is used to express the duration of time.
We can also use a dependent clause (subject+verb) after since:
...we got married
...I moved to New York
...he quit his job
or a gerund
...buying our new house
...writing my first book
Since is used to express a specific point in time.
Using the Past Tense with Since
Note that when using since, we sometimes use a combination of the present perfect in the independent (or main) clause and the past in the dependent clause. Take a look at these examples:
They haven't seen their grandmother since the family went on vacation last year.
present perfect past
Since I moved to Lisbon, I haven't eaten pancakes.
past present perfect
We can also use the gerund in the dependent clause, which gives the sentence a more general time frame and doesn't overtly identify the subject:
Since having a baby, she has lost weight quickly.
gerund present perfect
We haven't seen them since visiting last Christmas.
present perfect gerund
If you have any questions, just post below...I hope these tips help you!