In the field of logic, subcontrary expresses a specific relationship between two statements;
specifically, subcontrary statements are ones that cannot both be false.
A) Some X are animals.
B) Some X are not animals.
If X = 'cats', A is true. If X = 'carrots', B is true. And if X = things in my house, A and B are both true. There is no X for which one of these is not true. These statements are subcontrary.
In classical logic this was one of the four relationships possible between propositions, as observed in the square of opposition. The others are contradictory, contrary, and subalternation.
Brevity Quest 2016