Theories of language change usually focus on the question of change. Not less interesting is, however, the question of what does not change, which comprehends two aspects: (i) the general problem of stability, i.e. the general question of what conditions obtain when no change takes place, and (ii) the concrete historical problem of why a certain change X at a certain time and in a certain variety did not take place.
The chapter will approach these questions by making reference to the relative particles so and wo, which underwent opposite developments: five conditions – two of a general and three of a rather specific historical nature – can be made responsible for their development, which shows that language change can only be understood by taking into consideration sociopragmatic and variation-related factors.