strange pattern "...because of which ..."

[hairstyler]

Dear Carillo,

Please help me describe if the pattern "....because of which ..." exists.
I rarely see the pattern.

Thanks,
Hairstyler

[Joe Carillo]

Yes, the pattern “because of which” exists and is legitimate usage in English grammar. It means “on account of which,” as in this sentence: “I regret reading that horror novel, because of which I hardly slept last night.” Note that the comma before the subordinate clause is a must in such constructions in the same way as in its equivalent sentence using “on account of which”: “I regret reading that horror novel, on account of which I hardly slept last night.”

Without that comma, both "because of which" and "on account of which" constructions become dysfunctional, turning into run-on sentences:

“I regret reading that horror novel because of which I hardly slept last night.”
“I regret reading that horror novel on account of which I hardly slept last night.”

[Michael E. Galario]

Because of which is synonymous with because of that. just my two cents.

[Joe Carillo]

“Because of which” may seem and look like it’s synonymous with “because of that,” but the similarity ends there. Their syntax is actually different. Indeed, we can effortlessly say “I regret reading that horror novel, because of which I hardly slept last night” but not “I regret reading that horror novel, because of that I hardly slept last night,” which reads and sounds awkward. We’d be much better off rewriting the latter sentence as the more fluid “I regret reading that horror novel; I hardly slept last night because of it.”