Die Agensphrase mit "von" und "durch" beim persönlichen Agens in Passivsätzen

According to some grammars of German the agent can be lexically added to the passive predicate both with the preposition 'von' and 'durch' without a distinct difference in meaning. These grammars do not forbid the use of such passive sentences as 'Eva wird durch Hans geliebt' or 'Buecher werden vor allem durch Frauen gelesen'. The use of the preposition 'durch' in such cases seems very unusual and may be considered ungrammatical. In such cases the search in a big corpus can be very useful. This article presents statistical support for arguing that the use of the preposition 'durch' in passive sentences with a personal agent (human, animal or institution) is ungrammatical in many cases. It can only be used if the agent is subjectively presented - in sentences like 'Im 5. bis 6. Jahrhundert wurden die Alemannen durch die Franken verdraengt' - as a sort of means.