Certain sentence types require inverted word order, in which a verb is placed before the subject. These types include interrogative sentences, conditional clauses without if, and declarative sentences that begin with negative or restrictive words such as never, rarely, scarcely, hardly ever, and not only.
Do you understand Finnish?[interrogative]
Were she available, we would surely invite her.
Not only is the standard American aluminum can light in
weight and rugged but it is also about the same height and diameter as the
traditional drinking tumbler. [beginning with negative, not
--William Hostold and John Duncan, "The Aluminum Beverage Can," Scientific American