All B is C A teacher is a man, (A)
∴ All A is C ∴ T. Arnold was a man. (A)
All C is D A man is a biped, (A)
∴ All A is D ∴ T. Arnold was a biped. (A)
All D is E A biped is an animal, (A)
∴ All A is E ∴ T. Arnold was an animal. (A)
In the three completed syllogisms it becomes evident that the progressive sorites uses the minor as its first premise and in consequence takes the form of the fourth figure, though the reasoning is according to the first figure.
The progressive sorites must conform to the following rules:
(1) The first premise may be universal or particular, all the others must be universal.
(2) The last premise may be affirmative or negative; all the others must be affirmative.