Brown and Gilman argued that the choice of form is governed by either relationships of "power" or "solidarity", depending on the culture of the speakers, showing that "power" had been the dominant predictor of form in Europe until the 20th century. Thus, it was quite normal for a powerful person to use a T-form but expect a V-form in return. However, in the 20th century the dynamic shifted in favour of solidarity, so that people would use T-forms with those they knew, and V-forms in service encounters, with reciprocal usage being the norm in both cases.