Questions & Answers about Missä koira on, sisällä vai ulkona?
Why do we use vai here for "or" instead of tai?
In Finnish, there are two words for "or". You must use vai in questions when giving the listener specific, mutually exclusive options to choose between (the dog is either inside or outside, but not both). You use tai in normal statements.
How would this sentence change if it were a statement rather than a question?
If you were just stating a fact ("The dog is inside or outside"), you cannot use vai. You would switch to tai and say: Koira on sisällä tai ulkona.
Why do the words for "inside" and "outside" have the endings -llä and -na (sisällä, ulkona)?
Finnish expresses location by adding endings to the ends of words. Sisällä comes from the root sisä- (inner) plus the -llä ending (on/at). Ulkona comes from ulko- (outer) plus the -na ending. At this level, it is perfectly fine to just memorize sisällä and ulkona as fixed vocabulary words.
Is the word order Missä koira on normal, or should it be Missä on koira?
Both are completely correct! Finnish word order is very flexible. Missä koira on? is an extremely common and natural way to ask this in everyday speech, even though the literal English translation is "Where the dog is?".