← The hardest concepts in United States law
In one breath
When parties put their agreement into a final written form, the parol evidence rule bars evidence of earlier agreements or negotiations offered to contradict, and sometimes to add to, that writing. It does not stop evidence used to explain ambiguous words, to show fraud or mistake, or to prove a later change.
The picture
The napkin sketch and the signed blueprint
A couple sketches their dream house on a napkin over dinner, with a pool, a study and a two-car garage. Months later they sign the architect’s final blueprint, which shows no pool and a one-car garage. The builder is bound by the blueprint. The couple cannot wave the napkin to demand a pool, because the blueprint was meant to be the final statement of the plan. Whether the napkin can be used at all depends on how complete the blueprint was meant to be. If it says it is the entire plan, even a napkin detail that merely adds something is shut out. If it is only the main plan, a consistent extra such as the paint color may come in, but never a detail that contradicts it.
The napkin is not banned for every purpose. It can help explain a word the blueprint uses ambiguously, such as what “study” was meant to include. It can show that the blueprint was signed because of a trick. It can show that something had to happen before the blueprint took effect. And it cannot be used against what the couple agreed after the blueprint was signed, because later changes are a separate matter.
Where the picture stops working
A blueprint is a physical object, while integration is a legal conclusion about what the parties intended, reached by a judge, and courts disagree about how to reach it: some look only at the writing, others at the surrounding circumstances. The rule is also not truly a rule of evidence. It decides which agreement counts as the contract.
How it really works
- 1Ask whether there is a writing intended as the final expression of at least some of the terms. A merger clause is strong evidence of this, but not conclusive.
- 2Ask whether the writing is completely integrated (the whole agreement) or only partially integrated. The judge decides, and jurisdictions differ about what the judge may consider.
- 3Earlier agreements that contradict an integrated writing are barred. If the writing is completely integrated, even consistent additional terms are barred. If it is partial, consistent additional terms may come in (Restatement (Second) of Contracts sections 213 to 216; UCC section 2-202 for goods).
- 4Check the exceptions: ambiguity, fraud, duress, mistake, illegality, a condition that had to be met before the writing took effect, and agreements made after the writing.
- 5Separate interpretation from variation. Evidence that explains what the words mean is treated differently from evidence that changes what they say.
Why people get it wrong
- Calling it a rule of evidence only. It is a rule of substantive contract law about which agreement binds.
- Treating a merger clause as the end of every argument. It does not stop claims of fraud or mistake.
- Believing it excludes all evidence of earlier dealings. Such evidence may be admissible to interpret, and the extent differs between courts.
- Applying it to later agreements. A modification made after the writing is not barred by the rule, although other rules may apply.
- Taking “parol” to mean only spoken. Earlier drafts and letters are caught too.
A worked example
The facts are invented
Jun buys a used van from Kwame, a dealer. The signed contract describes the van and the price and says it is the entire agreement. Jun says that before signing, Kwame orally promised a year of free servicing. The writing is completely integrated, and the promise is an additional term not in it, so the evidence is excluded. Change the facts: the form is a one-line receipt with no merger clause. A court might find it only partially integrated and, if free servicing is a term the parties might naturally have left off a receipt, let the promise in.
Now suppose Jun says Kwame lied about the van’s accident history to get him to sign. The rule does not shut out proof of fraud. Suppose the contract promises delivery “in spring” and evidence of trade usage shows that dealers use the word to mean March to May. That helps interpret an ambiguous word and can be considered. What Jun cannot do is use any of this to substitute a different price from the one written.
Try it
Two parties sign a final written contract for the supply of goods. A few weeks later they orally agree to change the delivery date. Does the parol evidence rule bar proof of the oral change?
Landmark authorities
Read the sources themselves; this list is a starting point.
- Restatement (Second) of Contracts, sections 213 to 216
- Uniform Commercial Code, section 2-202
- Masterson v. Sine, 68 Cal. 2d 222, 436 P.2d 561 (1968)
- Pacific Gas & Electric Co. v. G.W. Thomas Drayage & Rigging Co., 69 Cal. 2d 33, 442 P.2d 641 (1968)
Where to go next
More hard concepts in United States law
- The battle of the forms (UCC 2-207) (Contracts)
- Promissory estoppel (Contracts)
This page is an educational overview. It is not legal advice and not a substitute for the sources: the statute, the rule, the case itself. United States law is made in fifty states and in the federal system, and the rules differ between them. Each page states the usual formulation of the rule and names landmark decisions; your own state, circuit or course may use different wording. Check the primary sources before relying on any rule.