MODEL VALIDATION IN SOFT SYSTEMS PRACTICE

The concept of 'a model' usually evokes the connotation 'model of part of the real world'. That is an almost automatic response. It makes se nse especially in relation to the way the concept has been developed a nd used in natural science. Classical operational research (OR), with its scientific aspirations, and systems engineering, use the concept i n the same way and in addition use models as surrogates for the real w orld, on which experimentation is cheap. In these fields the key featu re of a model is representativeness. In soft systems methodology (SSM) models are not of part of the world; they are only relevant to debate about the real world and are used in a cyclic learning process. The p aper shows how the different concepts of validation in classical OR an d SSM lead to a way of sharply defining the nature of 'soft OR'.