6. UNITY OF PRIMARY LAWS OF THOUGHT ILLUSTRATED BY SYMBOLS.
| (1) Absolute Symbols | Relative Symbols. |
| Excluded middle. | |
| A is either A or not-A. | A is either B or not-B. |
| Contradiction. | |
| A is not not-A. | A is not B or A is not not-B. |
| Identity. | |
| A is A. | A is not-B or A is B. |
| (2) Propositions made to fit symbols. | |
| Excluded middle. | |
| A man is either a man or a not-man. | A man is either honest or not-honest. |
| Contradiction. | |
| A man is not a not-man. | A man is not honest, or a man is not not-honest. |
| Identity. | |
| A man is a man. | A man is not-honest, or a man is honest. |
The “excluded middle” propositions of the foregoing express alternatives which are mutually contradictory. There is no middle ground. The “contradictory propositions” contradict the identity of the subject with one alternative, while the “identity” propositions affirm the identity of the subject with the other alternative. This is made possible because of the principle, “Of two mutually contradictory terms, if one is true the other must be false.” The foregoing scheme shows how closely “contradictory” and “identity” propositions are related to “excluded middle” propositions. Expressed mathematically: excluded middle = contradiction + identity.