On the example of physics, we show that the traditional one-level description is not completely adequate. For a more adequate structure, a hierarchical description of uncertainty is necessary, which supplements the more traditional first-order uncertainty with second-order, third-order and more sophisticated models. In particular, the second-order approach seems to provide a bridge between probabilistic and fuzzy approaches to uncertainty.
Hung T. Nguyen, Vladik Kreinovich, Luc Longpr&eacu