Uncertainty and type-2 fuzzy sets and systems

As part of this paper we are highlighting several - in our opinion- important aspects of type-2 fuzzy logic systems which seem important to its future development and application. It is the aim of the paper to provide more questions and more suggestive points than actual answers. With type-2 fuzzy logic and its application to modelling and handling uncertainty still a very young area of research, most answers are bound yet to be discovered.