For vs Since - Medium Exercises

At B1 level, for and since appear with less obvious time phrases and with present perfect continuous forms. Use for with full or approximate durations: for ages, for a couple of weeks, for the whole summer. Use since with a point, event, or clause that marks the beginning: since the start of term, since we moved, since she graduated. Approximate expressions still count as durations if they measure how long something has continued.

Present perfect continuous often describes an action that started in the past and is still in progress: "I have been studying for two hours" or "I have been studying since breakfast." The structure does not decide the preposition by itself. The following time phrase decides it. Look for words that measure time, such as weeks or ages, and words that introduce a starting point, such as since we last met or since the beginning. This keeps the choice stable even when the sentence has several clauses.