Express term of contract is more important that implied terms. Is it true? Why?

Express terms are normally given precedence because the court presumes that parties have given due consideration before setting their signatures onto the papers. This is the general rule and will always appear to be the case. Also, there is normally a term in the contract which says that any variation to the terms in the contract may only be made in writing. In situations where there are vagueness as to the standard procedure mentioned in the contract (ie where there are no further elaboration), court will look at the implied terms (ie the methods of practice by both parties. How have they dealt with one another in the past)? You are not answering an assignment question, are you? :)Express term of contract is more important that implied terms. Is it true? Why?
Terms formally written on the contract is valid as against implied terms under the Civil Law.Express term of contract is more important that implied terms. Is it true? Why?
Because it's clearer to known which is the part of contact and which doesn't.