Any pre-contractual material which the parties wish to be incorporated into the contract need to be assembled with it or explicitly referred to in the contractual documentation.
[2] Many modern cases, however, have found merger clauses to only a rebuttable presumption that the contract is integrated.
[3] In the United States, the existence of such a term is normally not conclusive proof that no varied or additional conditions exist with respect to the performance of the contract beyond those that are in the writing, but instead is simply evidence of that fact.
[5]Parties in dispute may wish to argue that a previous understanding or implied agreement, made before a contract with an entire agreement was signed, should also be separately enforced as a collateral contract.
Christopher Nugee QC, now a Lord Justice of Appeal, has ruled that the existence of an entire agreement clause within the main contract creates an "obvious difficulty" for a party who wishes to rely on such a separate agreement.