Amendment, addendum, side letter or restatement — which one you need

The four labels get used interchangeably, and courts look at what a document does rather than what it is called. Picking the right shape still saves an argument, because each answers a different question.

Four instruments, four jobs

• Amendment. Changes language already in the agreement — a price, a date, a scope item. It only makes sense read alongside the original.
• Addendum. Adds something the original did not deal with: a deliverable, a site, a schedule. The cleaner choice when you are extending rather than editing.
• Side letter. A separate agreement between the same parties recording a concession one of them does not want in the main document — a rebate, a waiver, an assurance. It binds, but it is easily lost when the contract is later assigned or restated.
• Amended and restated agreement. A full replacement folding every prior change into one clean text. Worth doing once there are three or more amendments, because at that point nobody can reliably state what the contract says.

None of them is a novation. If a different party is taking over, that is a change of who is bound rather than of what they are bound to, and it needs the incoming party, the outgoing party and the counterparty to sign. An addendum naming a new company rarely achieves it cleanly — in a rental agreement, adding an occupant and substituting a tenant are very different documents.

Does a "no oral modification" clause actually work?

It depends where you are, and the English answer changed within the last decade. In England and Wales the clause now works: in Rock Advertising Ltd v MWB Business Exchange Centres Ltd [2018] UKSC 24 the Supreme Court held that a requirement for variations to be in writing and signed made a later oral variation ineffective. Lord Sumption's reasoning was that party autonomy runs up to the moment the contract is made; after that the parties are bound by the formalities they chose. Estoppel survives as a narrow safety valve, but not one wide enough to swallow the rule.

In the United States it is statutory and varies by state and subject matter. For sales of goods, UCC § 2-209(2) provides that a signed agreement excluding modification except by signed writing "cannot be otherwise modified or rescinded" — with the protection that on a merchant's own form, the clause must be separately signed by a non-merchant. New York General Obligations Law § 15-301 does the same job for written contracts generally. California takes the opposite line: Civil Code § 1698 lets a written contract be modified by an oral agreement "to the extent that the oral agreement is executed by the parties", and by one supported by new consideration unless the contract expressly says otherwise.

The unsigned addendum in the email thread

This is by far the most common way a change fails. Someone drafts the addendum, circulates it, both sides say "looks good", the work changes on the ground, and nobody executes the document. It happens most on scope: a client asks for extra deliverables under an independent contractor agreement or a fixed-fee consulting agreement, the work is done, the fee was never papered, and a year later the payer points at the original.

The outcome is less predictable than either side expects, which is the problem. Under New York law an email chain can itself be the signed writing: in Stevens v. Publicis, S.A. (N.Y. App. Div., 1st Dept, 2008) emails in which each sender typed their name at the foot satisfied a contract requiring signed written modifications, because the typed name showed an intent to authenticate. So the thread may bind you where you assumed it could not — and may not, if it left terms open or the sender lacked authority.

The rule that follows: never rely on an agreed-but-unexecuted change. If you are already performing to it, get it signed this week. If they will not sign, write recording what was agreed and that you are performing on that basis — not an amendment, but the evidence you will need. Electronic execution is fine for almost every commercial document — are electronic signatures legally binding covers the handful of exceptions.

Does an amendment need consideration?

A promise to do what you were already obliged to do is not good consideration, so a variation benefiting only one side can be vulnerable. Three routes get round it.

• For sales of goods it is legislated away: UCC § 2-209(1) says a modification within Article 2 "needs no consideration to be binding". Good faith is still required.
• For everything else, add something small and real on the other side — a shortened payment term, an extra day, a nominal sum — and the objection disappears.
• In England, a variation executed as a deed needs no consideration at all, which is the standard fix where one party is genuinely giving something for nothing.

One caution on backdating. Recording that an amendment takes effect from an earlier date is normal and lawful; writing a false date in the signature block is not — effective date vs signature date sets out where the line falls.

Writing one that binds

1. 1

   1. Read the variation clause first

   It sets the form: writing, signature, sometimes named signatories or a requirement that the document call itself a variation. Whatever it says is the standard you have to meet, so read it before drafting.

2. 2

   2. Identify the original precisely

   Parties by their full legal names as they appear in the original, the title of the agreement, and its date — the date in the original's heading, not the day the last person signed. List any prior amendments in order.

3. 3

   3. Quote the words you are changing

   Clause number, then "is deleted and replaced with the following", then the new text in full. Never a narrative description: "the fee is increased" leaves the old wording standing and produces two readings of one contract.

4. 4

   4. Give it its own effective date

   From what date the change operates, and whether it reaches work already in progress. This is the most-omitted line in amateur amendments.

5. 5

   5. Confirm everything else is unchanged

   A short clause saying the original remains in full force and effect except as amended, closing off any argument that the amendment reopened terms it never mentioned.

6. 6

   6. Say which document wins on a conflict

   One sentence: on any conflict between this amendment and the original, this amendment prevails. Without it you are relying on interpretation, and interpretation costs money.

7. 7

   7. Have it signed by people who can bind the parties

   Same authority standard as the original. If a company is signing, use the company signature block — signing on behalf of a company shows the wording that keeps the signatory out of it personally.

When the amendment and the original conflict

It happens anyway — a schedule nobody updated, two clauses that now give different deadlines.

A specific term usually beats a general one and a negotiated term usually beats standard wording, but neither is a rule to depend on. Fix a conflict while the relationship is still healthy, with a further short amendment.

The part that is actually about filing

Almost every failure here is administrative rather than legal. The change was agreed by people with authority, on terms nobody disputes, and it fell over because the document was never signed, or was signed and never filed, or was filed under a name the next person did not recognise. Numbering amendments in sequence, storing them with the contract and recording the current position in one place prevents more disputes than any drafting refinement. So when the other side asks for a change verbally and starts performing to it, treat that as a deadline rather than a favour: the party who benefits from an unrecorded variation is whichever one later decides to deny it.