Georg Simmel 
The Sociology of Secrecy and of Secret Societies 

"That we shall know with whom we have to do, is the first precondition of having anything to do with another. The customary reciprocal presentation, in the case of any somewhat protracted conversation, or in the case of contact upon the same social plane, although at first sight an empty form, is an excellent symbol of that reciprocal apprehension which is the presumption of every social relationship."