です

[ningen]

Is the correct sentence これはいくらですか or これわいくらか?
'cause my knowledge of the grammar says that I can't use です here, but a website I found says I can.

(sentence is "How much does this cost?" right?)

 

[charusu]

Japanese is a SOV language (Subject Object Verb), gramatically correct sentences MUST MUST MUST end in a verb or a conjugated adjective. Here, desu is the verb, so the sentence MUST end in desu. Or da, since da is the informal form of desu.

I would not trust the online source you are using.

The aforementioned grammar is true independent of whether or not the sentence is declarative or interrogative, obviously making a sentence interrogative entails appending the sentence (that ends in a verb) with the interrogative particle (ka). Thus, これはいくらですか? is absolutely correct.

 

[Glenn]

これはいくらか (not わ) isn't grammatically wrong, but it's not very polite and pretty blunt. More common, if not using です, would be これはいくら?

 

[ningen]

I learned that in a question you don't use です, unless you use questioning words like だれ or どこ. In this sentence the か makes it a question, so then you don't add です right? that's at least what I thought

and the わ was a typo, sorry about that

 

[Half-n-Half]

いくら is a question word (How much?) It should be これはいくらですか。

 

[charusu]

No ningen, you always need the verb at the end. Even Google Translate will tell you that.これはいくらですか。is correct (my previous sentence is somewhat less correct in that there is no question mark in formal Japanese)

 

[Mike Cash]

I learned that in a question you don't use です, unless you use questioning words like だれ or どこ. In this sentence the か makes it a question, so then you don't add です right? that's at least what I thought

Either you learned wrong or somebody taught you wrong. Unfortunately, the web is full of blind-leading-the-blind Japanese learning sites thrown together by zealous beginners eager to share their meager treasure troves of knowledge. This is part of why the web will never be a good substitute for good pedagogically sound textbooks.

If you're going to leave desu out of questions, then leave out the ka as well and just rely on intonation to denote a question. Later on in your studies you'll encounter things like だれか なにか いつか etc, which don't mean "who?", "what?" or "when?" but instead mean "someone", "something", and "sometime".

 

[Toritoribe]

In addition, これいくら？ is also quite commonly used in casual conversation.