'Some students are sincere' is an example of which proposition?

Some students are sincere is a particular affirmative proposition.

The word some limits the quantity to part of the subject class, making it particular.

The verb are affirms the predicate of that part, giving it affirmative quality.

Particular quantity joined with affirmative quality yields a particular affirmative proposition.

Only a portion of the students is asserted to be sincere.