Think of the parol evidence rule as being similar to Janus, the figure from Roman mythology, who was guardian of portals and patron of beginnings and endings.He faced both ways at once, symbolizing his power to let in or keep out the muses.So the parol evidence rule acts as a guardian of the gate of contract.The exclusion face of the rule states that the writing is intended to express the final intent of the parties.

Because the bottom line is to make sure that equity is done, there is both a public policy and practical necessity of having exceptions to the parol evidence rule-why?