What Is Their Main Difference?
'For' and 'since' have the same parts of speech. They are both prepositions, subordinating conjunctions, and adverbs. However, 'for' refers to a period of time. It can be in the past, in the present, or in the future. 'Since', though, indicates a particular point in the past continuing to the present moment.
As stated above, 'for', basically shows the duration of something. It can be in the past, in the present, or in the future. Look at the examples below:
I've been a ballet teach
When Mark went into his room, he cried
'Since', on the other hand, signifies a particular point in time and continues to the present moment. Let us take a look at the examples below:
You have tolerated his abusive behavior
As stated above, they both have the same parts of speech. They are prepositions, subordinating conjunctions, and adverbs. Check out the following examples:
I used to work at a museum
Here, 'for' is a preposition.
I cannot think of anything right now
Here, 'for' is a subordinating conjunction.
Most people voted
In this examples, 'for' is an adverb.
Now, let us analyse the different functions of 'since':
Here, 'since' is a subordinating conjunction.
The couple have been arguing
Here, 'since' is a preposition.
We met this week, and we've been having fun with each other ever
Here, 'since' is an adverb.
Are They Interchangeable?
Although they have the same grammatical functions, they cannot be used interchangeably. Compare:
✓ I've been dealing with these emotions
X I've been dealing with these emotions
As you can see, this sentence is grammatically incorrect.