Originally Posted by
margora
"You definitely do not strike just one string on purpose".
Actually, you do, and contrary to the majority of the comments above, it is not a mistake.
The "single string on the upstroke" dates back to 18th century mandolin methods (Gabriele Leone, in particular, in 1768) and is a mainstay of modern German classical mandolin technique. It is used, for instance, in situations where a "strong-weak" accent pattern is desired, or at the end of a musical phrase whenever a lighter texture is musically appropriate. The technique is discussed extensively in Marga Wilda-Husgen's mandolin method (also in Getrud Weyhofen's "Music on Eight Strings") and also, if my memory is correct (I am at work) in Caterina Lichtenberg's excellent new Homespun video on classical mandolin technique. There is a special notation symbol to use if the composer wishes although in most cases it can be left to the discretion of the performer. In his workshop at the Classical Mandolin Society meetings last fall in Baltimore Chris Aquavella covered the technique. Nowadays, it is a very basic skill in classical mandolin, at least for those coming from the German side of things.