Breakdown of Är idén inte alls innovativ? Jo, men den är befängd.
vara
to be
den
it (common)
inte
not
men
but
Questions & Answers about Är idén inte alls innovativ? Jo, men den är befängd.
Why do we use inte alls here instead of ingen alls or inget alls?
In a question like this, does alls have to come immediately after inte?
Yes. As a set phrase meaning "at all," inte alls stays together. In Swedish questions, the negation comes after the subject, so it must be Är idén inte alls innovativ? You cannot put alls at the very end of the sentence like you do in English.
Why does the answer start with Jo instead of Ja?
Jo is specifically used to mean "yes" when contradicting a negative statement or answering a negative question. Since the first speaker asks Är idén inte alls innovativ? (Is the idea not innovative at all?), answering with Jo means "Yes, on the contrary, it is innovative."
Why does the sentence use befängd instead of befängt?