| Paragraph 1 | Demonstration per impossibile differs from ostensive proof in that it posits what it wishes to refute by reduction to a statement admitted to be false; |
| Paragraph 2 | Again suppose it has been proved in the middle figure that A belongs to all B. |
| Paragraph 3 | Again suppose it has been proved in the third figure that A belongs to all B. |
| Paragraph 4 | It is clear then that it is possible through the same terms to prove each of the problems ostensively as well. |
HTML by 
created 1996/11/25 modified 2009/04/26