Full Idea
Since to belong, to belong of necessity, and to be possible to belong are different, ..there will be different deductions for each; one deduction will be from necessary terms, one from terms which belong, and one from possible terms.
Gist of Idea
There are three different deductions for actual terms, necessary terms and possible terms
Source
Aristotle (Prior Analytics [c.328 BCE], 29b29-35)
Book Reference
Aristotle: 'Prior Analytics', ed/tr. Smith,Robin [Hackett 1989], p.13
A Reaction
Fitting and Mendelsohn cite this as the earliest thoughts on modal logic. but Kneale and Kneale say that Aristotle got into a muddle, and so was unable to create a workable system.