A Venn diagram consists of circles or other simple geometric shapes that can be completely separate, overlap or completely encompass each other. Two circles, A and B, that do not touch at all correspond to the statement “if something is in A then it is not in B.” A and B crossing corresponds to “If something is in A, it might be in B.” Circle A drawn entirely within circle B corresponds to two possible statements: “If something is in B, it might be in A,” and “If something is in A, then it is definitely in B.”
You can illustrate the statement “If an animal is a fish, then it is not a bird” by one circle representing fish, and a separate circle representing birds. “If an animal can’t fly, it might have feathers” corresponds to a circle for animals that do not fly crossing a circle for animals that have feathers. The part where they cross contains animals such as ostriches and penguins. “If an animal is a fish, it lives in water” corresponds to a circle for fish within a circle for animals that live in water.