'Since' can mark the starting point of a period of time up to now. 'Since' can also introduce a reason or explanation. The meaning is decided by whether the clause refers to time or gives a cause.

Word/Phrase	Definition
since	'Since' marks when something began and connects it to now.
since	'Since' introduces a reason or explanation.
for	'For' expresses the length of a period, not the starting point.

When 'since' marks time, it connects a starting point to the present or another time. It often appears with present perfect or past perfect because these tenses link past and present. The clause after 'since' gives the start, and the main clause describes the ongoing result.

Rule
Use 'since' to show when a situation started and is still true.
Use present perfect with 'since' to link past start to now.
Use past perfect with 'since' to link a past start to a later past event.

After 'since', the starting point can be a specific time, a date, an event, or a completed action. The key idea is that 'since' points to when something began, not how long it has lasted. The rest of the sentence usually describes a state or result that continues.

Word/Phrase	Definition
Monday	A named day used as a starting point with 'since'.
2010	A year or date used as a starting point with 'since'.
I arrived	A completed action used as a starting point with 'since'.

When 'since' means 'because', it introduces a reason for the main clause. This use does not focus on time and often works like 'because' in meaning. In writing, 'since' for reason is common when the reason is already known or less important than the result.

Rule
Use 'since' to introduce a reason when explaining a result.
In reason clauses, 'since' acts like 'because' in meaning.
In reason clauses, the main point usually comes after 'since'.

With 'since', you can place the 'since' clause before or after the main clause. If the 'since' clause comes first, it is usually followed by a comma in writing. The main clause carries the main information, and the 'since' clause adds time or reason.

Rule
A 'since' clause can come before or after the main clause.
When the 'since' clause comes first in writing, use a comma after it.
The main clause gives the main message; the 'since' clause adds background.

With 'since' for time, present perfect is common when the result continues to now. Past perfect is used when both the start and the result are in the past. Simple past is not usually used with 'since' to describe a continuing situation.

Rule
Use present perfect with 'since' for a situation that continues to now.
Use past perfect with 'since' for a situation that continued up to a past point.
Avoid simple past with 'since' if the situation is meant to be ongoing.

'Since' marks a starting point in time or introduces a reason. For time, it works with present perfect or past perfect and points to when something began. For reason, it explains why something is true and often functions like 'because'. Choosing the correct meaning and tense makes sentences clear.