is logically equivalent to:
IF Target_Far THEN Desirable
OR
IF Ammo_Loads THEN Desirable
Using this principle, a rule base can be defined that contains only one rule
per consequent member set. For example, the nine rules for the desirability
of the rocket launcher given previously:
Rule 1. IF Target_Far AND Ammo_Loads THEN Desirable
Rule 2. IF Target_Far AND Ammo_Okay THEN Undesirable
Rule 3. IF Target_Far AND Ammo_Low THEN Undesirable
Rule 4. IF Target_Medium AND Ammo_Loads THEN VeryDesirable
Rule 5. IF Target_Medium AND Ammo_Okay THEN VeryDesirable
Rule 6. IF Target_Medium AND Ammo_Low THEN Desirable
Rule 7. IF Target_Close AND Ammo_Loads THEN Undesirable
Rule 8. IF Target_Close AND Ammo_Okay THEN Undesirable
Rule 9. IF Target_Close AND Ammo_Low THEN Undesirable
can be reduced to six rules:
Rule 1. IF Target_Close THEN Undesirable
Rule 2. IF Target_Medium THEN VeryDesirable
Rule 3. IF Target_Far THEN Undesirable
Rule 4. IF Ammo_Low THEN Undesirable
Rule 5. IF Ammo_Okay THEN Desirable
Rule 6. IF Ammo_Loads THEN VeryDesirable
This is not a great reduction of course, but as you saw in Table 10.4, the
Combs method becomes an increasingly attractive alternative as the num

ber of member sets used by the linguistic variables rises.
One of the drawbacks with this method is that the changes to the rule
base required to accommodate the logic are not intuitive. Combs gives a
good example in his paper “The Combs Method for Rapid Inference”:
When I got my first driver’s license, my insurance agent reminded me
that since I was sixteen AND male AND single, my insurance premium
would be high. Later, after college, he said that since I was in my
midtwenties AND male AND married, my insurance premium would be
moderately low.
This latter statement seems to make more intuitive sense than our alter

native format: since I was in my midtwenties, my insurance premium
would be moderately low, OR since I was a male, my insurance premium
would be moderately high, OR since I was married, my insurance pre

mium would be low.
Fuzzy Logic  453
The Combs Method