Following traditional models the difference between young and old would be marked by a clear line, let us say at the age of 35. Thus, a person would shift from young to old exactly at midnight of its 35th birthday.
Copyright: PSI FLS
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Fuzzy logic offers much better possibilities to represent the qualitative character of such kind of assignments or decisions. Instead of sharply defined limits between young and old, yes and no, or 1 and 0 (as in the classical logic) intermediate values are added to enhance the classical yes-no scheme.