Hello Mr.Jin Bae! I have a few questions about essential and nonessential..

First of all, do we consider other relative clauses except for "which" clause and "that" clause as essential or nonessential? The textbook says it really depends on, but it does not explain in detail. Moreover, the lecture does not include this part, though you explained everything else about essential and nonessential in other chapters.. If you really don't mind, could you pls elaborate this part?

Second question is.. how exactly do we connect an IC after DC?

In the lecture, you have briefly mentioned that normally we put nothing after IC when DC follows right away. However, I saw some other teachers always using commas between IC and the DC that comes right after. For ex) "I was doing my homework, while Tom was playing a game." In this sentence, "I was doing my hw" must be Ic and "while Tom was playing a game" must be subordinating clause, which is DC, right? Could you please explain me why do we have comma between them? 

By the way, I really love your lecture and it is one of the best lectures I have ever listened to, thank you so much!