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Let us be clear about time phrases beginning with "SINCE" and "FOR".

SINCE/FROM refers to POINT OF TIME    (10 a.m./year1940/Monday last)

FOR / FROM refers to PERIOD OF TIME (10 hours/ 3 days/ 4 months)

They have nothing to do with tenses. However, they assume special importance as 'perfect continuous' form of tenses specially demands mention of time factor.

" Since/for/ from" can safely be used in any other tenses if their presence can by no means disturb the basic concepts of time element of tenses in use.

As regards Present Perfect Tense, it is not a self contained tense; as if it expects some thing else of undefined nature. (e.g., I have sat for the exam.--just completed action--expecting may be result, may be outcome, may be any thing else) We may use since and from here as well.

Let us be clear about time phrases beginning with "SINCE" and "FOR".

SINCE refers to POINT OF TIME  (10 a.m./year1940/Monday last)

FOR / FROM refers to PERIOD OF TIME (10 hours/ 3 days/ 4 months)

They have nothing to do with tenses. However, they assume special importance as 'perfect continuous' form of tenses specially demands mention of time factor.

" Since/for/ from" can safely be used in any other tenses if their presence can by no means disturb the basic concepts of time element of tenses in use.

As regards Present Perfect Tense, it is not a self contained tense; as if it expects some thing else of undefined nature. (e.g., I have sat for the exam.--just completed action--expecting may be result, may be outcome, may be any thing else) We may use since and from here as well.

Let us be clear about time phrases beginning with "SINCE" and "FOR".

SINCE/FROM refers to POINT OF TIME   (10 a.m./year1940/Monday last)

FOR refers to PERIOD OF TIME (10 hours/ 3 days/ 4 months)

They have nothing to do with tenses. However, they assume special importance as 'perfect continuous' form of tenses specially demands mention of time factor.

" Since/for/ from" can safely be used in any other tenses if their presence can by no means disturb the basic concepts of time element of tenses in use.

As regards Present Perfect Tense, it is not a self contained tense; as if it expects some thing else of undefined nature. (e.g., I have sat for the exam.--just completed action--expecting may be result, may be outcome, may be any thing else) We may use since and from here as well.

1
source | link

Let us be clear about time phrases beginning with "SINCE" and "FOR".

SINCE refers to POINT OF TIME (10 a.m./year1940/Monday last)

FOR / FROM refers to PERIOD OF TIME (10 hours/ 3 days/ 4 months)

They have nothing to do with tenses. However, they assume special importance as 'perfect continuous' form of tenses specially demands mention of time factor.

" Since/for/ from" can safely be used in any other tenses if their presence can by no means disturb the basic concepts of time element of tenses in use.

As regards Present Perfect Tense, it is not a self contained tense; as if it expects some thing else of undefined nature. (e.g., I have sat for the exam.--just completed action--expecting may be result, may be outcome, may be any thing else) We may use since and from here as well.