1. The law of noncontradiction: A thing, A, cannot at once be and not be (A cannot equal A and equal non-A at the same time and in the same way); they are mutually exclusive (not both). A dog cannot be a dog and be a non-dog.
2. The law of excluded middle: A thing, A, is or it is not, but not both or neither (either A or non-A), they are jointly exhaustive—one of them must be true. There is no middle ground between a dog and a non-dog.
3. The law of identity: A thing, A, is what it is (A is A). A dog is a dog.