The three Laws of logic!
The law of identity
The law of noncontradiction
The law of the excluded middle
The law of identity
The law of identity states that given A, A=A. This principle is not formally present in Aristotelian writings, but from Parmenide (VI-V century BC) to stoics (III century BC) to Duns Scotus (13th century) it is the logical version of the fact that, during a reasoning, the meaning of the terms must remain constant.
The law of non-contradiction
In a statement one can not assert and deny a subject’s predicate at the same time and in the same sense. Aristotle expresses this as follows: “It is impossible that the same attribute at the same time belong to and not belong to the same object and in the same relationship” (Metaphysics IV, 1005b, 19-20).
The law of the excluded middle
states that in a two-value system, True and False, a statement is either true or false: a third possibility is excluded. This is a useful principle to infer a conclusion, say A, demonstrating that its opposite (non-A) is contradictory. They are of this kind the Reductio ad absurdum demonstrations.
The three laws of logic Law of logic also refer to the Basic laws of Propositional Logic or First Order Predicate Logic. Laws of thought, they present first principles before reasoning begins. Rules of inference, and dictate the valid use of inferential reasoning.
