We call these sentences rules of reasoning . They could be called reasoning axioms. An important class of these rules of reasoning are known as tautologies . A tautology is a sentence which is true no matter what the truth value of its constituent parts. We can show that this is a tautology from a truth table.
Every tautology is a rule of reasoning.
The following are tautologies that we commonly use. You will find these listed in the Rules of Logic that you have been given.