Language comparison
Some prerequisites
Identifying a language
Comparison as a scientific method
The tertium comparationis
What is the tertium comparationis in general comparative linguistics?
Zum Tertium comparationis im typologischen Sprachvergleich
Lawful connections in the object area
Implikative Generalisierungen
Implicational hierarchy
Corpus of translations
Here are some pages on problems of general comparative linguistics.