英语语法: “I will appreciate it/that if…” it 的作用
Source: Zhihu
(prepared by: alexcwlin; edited by: Adam Lam)

Question:
为什么I will appreciate it if you……一定要加个it呢?

为什么不能 I will appreciate that直接用宾语从句

alexcwlin comments:
Of course you can say “I will appreciate that if you try” instead of “I will appreciate it if you try”.

However, in “I will appreciate that if you try”, “that” is not a Subordinating Conjunction in introducing a Dependent Clause. “That” here is a Pronoun—Object of the Transitive Verb “appreciate”.

In both “I will appreciate that if you try” and “I will appreciate it if you try”, “if you try” is an Adverbial Dependent Clause introduced by the Subordinating Conjunction “if” modifying the Verb “appreciate” in stating that “appreciate” will happen when “you try”.

Actually, you can drop “it” or “that” in this sentence and make it “I will appreciate if you try”. Here “if you try” becomes a Noun Clause introduced by the Subordinating Conjunction “if”.

--------------------------