1. The Law of Identity - A is A Everything is the same as itself; or a statement cannot not remain the same and change its truth value.
2. The Law of Non-Contradiction - NOT (A and not A) Nothing can both exist and not exist at the same time and in the same respect; or no statement is both true and false.
3. The Law of Excluded Middle - Either (A or not A) Something either exists or does not exist; or every statement is either true or false.
These are given not just as nice rules of thumb to follow or ways that one should think. Aristotle identified these as necessary conditions for thought. People sometimes try to produce counter examples to these Laws by pointing out how statements can become true or false depending on the conditions; e.g. "It is raining" might be true now, but was false yesterday" or "it is half way between raining and not-raining." But these attempts always involve changing the reference of the statement. Once we get the reference of the statement clear and explicit, it does not seem possible for a statement to make sense and vioate these laws.