Affirmative conclusion from a negative premise

Affirmative conclusion from a negative premise is when you start with at least one "no" fact and then conclude something positive (e.g. "some X are Y"). In standard syllogistic logic, you can't get a positive conclusion from only negative premises—the two "no"s don't link things in a way that supports a "yes." The argument form is invalid.

Examples

• No fish are mammals. Some animals are fish. So some animals are mammals.

• No birds are reptiles. Some creatures are birds. So some creatures are reptiles.

• No students were late. Some people in the room are students. So some people in the room were on time.

• No members voted against. Some attendees are members. So some attendees voted in favour.