| Fig. ii. PM SM | Fig. iii. MP MS | Fig. iv. PM MS. |
It results from the doctrines of Conversion that valid arguments may be stated in these forms, inasmuch as a proposition in one order of terms may be equivalent to a proposition in another. Thus No M is in P is convertible with No P is in M: consequently the argument
No P is in M
All S is in M,
in the Second Figure is as much valid as when it is stated in the First—
No M is in P
All S is in M.
Similarly, since All M is in S is convertible into Some S is in M, the following arguments are equally valid:—
| Fig. iii. | = | Fig. i. |
| All M is in P | All M is in P | |
| All M is in S | Some S is in M. |
Using both the above Converses in place of their Convertends, we have—