∴ All C is B
All D is C
∴ All D is B
All E is D
∴ All E is B
By examining the foregoing it becomes apparent that the regressive sorites, both in form and in the reasoning, adapts itself to the first figure.
The rules of the regressive sorites are just the reverse of the progressive. These are:
(1) The first premise may be negative; all the others must be affirmative.
(2) The last premise may be particular; all the others must be universal.
It would be a valuable exercise for the student to test these rules according to the plan pursued in treating the progressive sorites.