X. A number of methods have been used to propagate probabilities during rule based inference. Many of these techniques are based on the probabilistic inference techniques used in Mycin and Prospector . The weakness of such techniques is that they do not reflect the way human experts reason under uncertainty. XpertRule KBS allows an alternative methodology to the probabilistic reasoning approach. This allows the expert to dictate the relationship between the symptoms and diagnosis, instead of relying on the mathematical propagation of probabilities.
Many people confuse the above example of uncertain reasoning with fuzzy reasoning.
On the other hand, Fuzzy Logic is concerned with the reasoning about 'Fuzzy' events or concepts. Examples of fuzzy concepts are 'temperature is high' and 'person is tall'. If we define the threshold of tallness at 180 cm, then the implication is that a person of 179.9 cm is not tall. When humans reason with terms such as 'tall' they do not normally have a fixed threshold in mind, but a smooth fuzzy definition. Humans can reason very effectively with such fuzzy definitions, therefore, in order to capture human fuzzy reasoning we need fuzzy logic.