Varieties of ignorance and the need for well-founded theories

The great danger in computer implementation of approximate reasoning is the use of inappropriate, unjustified, ad hoc models. Newcomers in the domain of commonsense reasoning could be overwhelmed by the multitude of models. Their reaction could be either to accept one of them and use it in every context or to use all of them somehow at random. Both attitudes are wrong. The stubborn use of one model is inappropriate as ignorance, uncertainty and vagueness are really different concepts. Random usage usually leads to inappropriate matching.