A distance-semantic is attached to fuzzy acceptabilities. Within the f
rame of this semantic, a modified version of the extension principle p
roves to be obligatory. It is derived without referring to fuzzy logic
and coincides only under certain assumptions with the usual version o
f the extension principle. Over that, it is shown under not very restr
icting assumptions that membership-functions which are compatible with
the above semantic have to be automatically of that triangle- or trap
ezoid type which is so popular in fuzzy applications.