Reason, Morality, Lying

Kant's four examples of 'duty' are often regarded as more interesting than rigorously convincing, primarily because of the difficulty in corresponding a logical contradiction with a concrete event.  Still, the example of false promising has been appreciated as more instructive than the others, since it entails both the construction and the breaking of a social convention.  But, that example is distinctive in another respect--it is fundamentally linguistic.  Hence, on that interpretation, false promising is a special case of lying, which is fundamentally immoral, because it undermines the effectiveness of language, the medium of communication, and, hence, it undermines the very basis of social harmony.