Abstract: A circuit (14) and method which determine a degree of membership of an input in a membership set during a fuzzy logic operation. The degree of membership is calculated by a single "MEM" software instruction. The MEM instruction determines whether the system input has a degree of membership of zero, of a saturation level, or of some value in between. If a membership function has a boundary with an infinite slope, the slope value is set equal to zero and the degree of membership is then set equal to a saturation value for those input values corresponding to the infinite slope boundary.