Hi

I have seen modifying phrase starting with with .
For example:

{removed example because it is copyrighted by OG}

Here with is acting as a adverbial modifier right ?

Second, Can we have a for starting a modifier phrase?

For example:
Historians and philosophers in the late 19th century both argued that Plato's work was perhaps the ultimate work of political philosophy, for it was the one paradigm of political discourse that could not be superseded.

Can you state a simpler example to help understand.

Thanks
DCE

Hmm. I think in your example you are using "for" as a conjunction connecting two full clauses, as opposed to a preposition introducing a modifier. You could construct a sentence like this:

"I like riding my bike FOR the exercise". This would be more analogous to your previous example (which I had to remove because it came from the OG and is copyrighted).

Note that adverbial modifiers will generally answer a question like "How?", "When?", "Where?", or "Why?" (but not "what"). Here, "for the exercise" answers the question of why I ride my bike.