「 〜のです。」is confusing when I have to use it with the casual form of the verb


I'm having trouble understanding the difference between 何かあるのですか。and
何かあったのですか。Are they both the **same**? Initially I thought that the former was
present tense and the latter was past tense but I really don't know. It's
confusing to me. Please explain...




あった is the past form of ある, so the difference is simple:

  * 何かあるのですか。  
Is there something?  
Is something going on?  
Will something happen?  
(Very literally: Is it that something exists?)

  * 何かあったのですか。  
Was there something?  
Did something happen?  
(Very literally: Is it that something existed?)

のですか/んですか/のか/の at the end of a question is for seeking clarification (known as
explanatory-no). See [this article](https://www.wasabi-jpn.com/japanese-
grammar/question-markers/) and [this
question](https://japanese.stackexchange.com/q/5398/5010). のだ/のです/etc itself
won't be in the past form even when you're talking about something in the
past.

