Intention - Element of Contract
Moreover to an agreement to constitute a contract then the parties thereto must have intended it for have legal consequences. Subsequently an agreement such contains an express declaration such it is not intended for have legal consequences as e.g. like the "Honourable Pledge Clause" in Rose and Frank V. Crompton Bros will not be enforced through the courts despite that its embodying all the other elements to a valid contract.
All over in practice further parties do not direct their attention for this point whether negotiating with each other thus with the consequence such the courts have but as it were been called upon for "fill the gaps". Hence they have done through formulating certain principles as such "presumptions" that will apply in such absence of an express declaration for the contrary.