The meaning of く

Question

I was browsing fairly random old questions to see if I could learn a few little things ( I could) and stumbled across this one-

The topic is the restaurant, or the conversation is at the restaurant?

I understand the main thrust of the question OK. That's not my problem here. Where I am slightly puzzled however is in the く after 新し.

はなしの種に、新しくできたレストランに食べに行ってみた。

I realise this is an idiotic question however I am very very bad at grammar. Even with English it is only after I spent a few months teaching the stuff that I learned what simple things like nouns and verbs are. I want to get from the stage of reading and understanding towards understanding every little thing in a sentence however.

I understand this く is something to do with 新しい　being a い adjective?　But...thinking about it I can only recall 新しくない as a reason for a く to interlude. But that clearly isn't the case here.

Why is this く necessary? Why would 新しいできた not do?

Answer 1

Adding the く to an i-adjective in this particular usage makes it function as an adverb so that you can use 新しい to modify できる. 新しく出来た means "newly completed."

Other examples might be 速く走る、遅く起きる、赤くなる, etc. With na-adjectives you would add に to it instead of く, like 綺麗に書く or 丁寧に切る.

Note that 新しく and its ilk are not what would be referred to as 副詞 in Japanese, which is the usual translation for an adverb. Using the く is a particular way of inflecting an adjective to make it function like an "adverb" in the sense that it modifies the following verb. It should also be noted that this form does not have to be used as an adverb. It can also be used as a form similar to the て form of a verb, for example.