Hello, fellas. How is life today? In this session we are going to learn about time signals frequently used in present perfect tense. They are since and for.
According to Betty Schrampfer Azar, present perfect tense mainly consists of have/has + past participle. It shows that an event occurred or never occurred before now. The time when the event took place is not important.
(More on present perfect tense: https://englishtips4u.com/2011/11/13/engclass-present-perfect-tense-vs-simple-past-tense/)
However, present perfect tense carries different meaning when since or for is used. Present perfect tense with since or for means that something happened in the past and continues to the present.
There is a difference between since and for. Since is followed by a particular time, while for precedes a duration of time.
1) Indonesia has existed since 1945.
2) The students have played football for an hour.
Betty Schrampfer Azar, Fundamentals of English Grammar: Third Edition
Betty Schrampfer Azar, Understanding and Using English Grammar: Third Edition