These deductions are all particular, whether affirmative (see Darapti, Disamis, and Datisi) or privative (see Felapton, Ferison, and Bocardo).
The fourth incomplete deduction is Datisi, using the same premises of Disamis, but in the inverted order: (51)
The additional assumption amounts to converting the minor premise "some S is R" into "some R is S," such that Datisi (3.4) is reduced to the complete deduction Darii (1.3) of the first figure:
With the change in the ordering of the terms, Datisi is made potentially complete owing to the inferential necessity (complete deducibility) of Darii.
we get the mode Datisi, which belongs not to the 4th figure, like Dimaris, but to the 3rd, which has the middle terms in the premises in a different location.
(b) Every linguist is a scholar and Some linguists are teachers (mode Datisi)