The rules in one line each
- "All A are B" puts A fully inside B
- "Some A are B" means at least one A is a B
- "No A is B" means the two sets do not overlap
Worked examples
Example 1. All A are B, and all B are C. Then all A are C; this must be true.
Example 2. All cats are animals; some animals are pets. We cannot conclude that any cat is a pet, because the pets among animals might not include any cats.
Method
Draw the diagram so as to make the conclusion false if possible. If you can, the conclusion does not definitely follow. Related topics: blood relations and number series. See the application in banking reasoning.