A predicate calculus will usually include all the same rules as a propositional calculus, with the addition of quantifiers such that if we take Φ to be a formula of propositional logic and α as a variable then we can take ( ∀ {\displaystyle \forall } α)Φ and ( ∃ {\displaystyle \exists } α)Φ each to be formulas of our predicate calculus.