There is a posted question about prepositions: "To which", "by which", "on which" etc. I could not add a comment because I have not had 50 reputations yet, so I decided to post another question.
It is the mechanism by which hospitals are reimbursed by Medicare.
I don't understand why there is by before the which, and why this by is added when there is already a by after the reimbursed.
"By" is a preposition in English that is frequently used to replace the instrumental case in Old English.
instrumental case: this case is expressed by inflection in Old English, Sanskrit, Russian, etc., and in English with the prepositions by or with (Ex.: OE ðȳ spere, “by the spear, with the spear”) Collins English Dictionary
With the collapse of the declension system in English, beginning a thousand years ago, prepositions were required to express the function of a noun or pronoun.
It is the mechanism by which hospitals are reimbursed by Medicare.
Hospitals are reimbursed . The means of this reimbursement is the mechanism; "which" refers to the mechanism.
"Which" (mechanism) can be thought of as the instrument of reimbursement .
This sentence could be writen differently:
By this mechanism hospitals are reimbursed by Medicare.
"Which" is gone.
So long as "which" is present, referring to "mechanism". the "by" is required to indicate the instrumental nature of "mechanism".
Without the "by":
It is the mechanism which hospitals are reimbursed by Medicare.
The "by" might be understood, but it might not . The second "by" (by Medicare) is a separate instrumental unrelated to "by which".
I will give you a simple answer.
It is the mechanism by which hospitals are reimbursed by Medicare.
Related:
Hospitals are reimbursed by Medicare by some certain mechanism.
The first part is the passive voice, equivalent to "Medicare reimburses hospitals."
The second part, "by some mechanism" could be restated as "through some mechanism."
