# Offer and acceptance: forming a contract

> **Key takeaway:** Offer = willingness to be bound on stated terms on acceptance. Invitation to treat (e.g. goods on shelf — Boots) is not an offer. Acceptance must be final and communicated; counter-offer kills the original offer (Hyde v Wrench). Battle of forms: often last shot (Butler Machine Tool). Unilateral offers: Carlill.

- **Jurisdiction:** England & Wales
- **Practice area:** Commercial
- **Last reviewed:** 2026-08-04
- **Interactive page:** https://kttclegal.info/library/notes/Commercial/offer-and-acceptance
- **Keywords:** offer and acceptance, invitation to treat, counter-offer, battle of the forms, Carlill, Boots, Hyde v Wrench, formation of contract

## What is this about?

A bilateral contract is formed when an offer is accepted with the requisite intention and (usually) consideration. Distinguishing an offer from an invitation to treat, and identifying when and how acceptance takes effect, remains foundational in commercial and consumer disputes — especially where negotiations are conducted by email, website checkout flows, or protracted correspondence.

## What is the core rule?

An offer is an expression of willingness to contract on specified terms, made with the intention that it will become binding as soon as it is accepted. Acceptance must be a final and unqualified assent to the terms of the offer, communicated to the offeror (subject to limited exceptions such as the postal rule where it still applies). A counter-offer rejects the original offer; a mere request for information does not.

## What are the elements or test?

1. Is there an offer (as opposed to an invitation to treat, supply of information, or preliminary negotiation)?
2. Has the offer been terminated before acceptance (revocation communicated to the offeree, rejection, counter-offer, lapse of time, or death in limited circumstances)?
3. Is there acceptance that is final and unqualified, matching the offer on material terms (mirror-image approach, subject to any course of dealing or battle-of-forms analysis)?
4. Has acceptance been effectively communicated (or does a recognised exception apply, e.g. postal rule for properly posted letters of acceptance where that rule has not been ousted)?

## Which authorities matter?

- **Carlill v Carbolic Smoke Ball Co [1893] 1 QB 256** — Classic illustration of a unilateral offer to the world at large and acceptance by performance; also addresses how certainty and intention can be inferred from the offeror's words and conduct.
- **Pharmaceutical Society of Great Britain v Boots Cash Chemists (Southern) Ltd [1953] 1 QB 401** — Leading authority that goods on supermarket shelves are generally an invitation to treat; the customer makes the offer at the till, accepted by the retailer.
- **Hyde v Wrench (1840) 3 Beav 334** — A counter-offer rejects the original offer so that it cannot later be accepted unless revived.
- **Butler Machine Tool Co Ltd v Ex-Cell-O Corp (England) Ltd [1979] 1 WLR 401** — Court of Appeal approach to the 'battle of the forms'; last shot often wins on traditional offer/acceptance analysis, though Lord Denning MR also discussed looking at the documents as a whole.

## How does this apply in practice?

This note covers bilateral and classic unilateral offer/acceptance. It does not cover consideration, intention to create legal relations, certainty of terms, or statutory controls on consumer contracts (e.g. CRA 2015). Electronic commerce and website terms often turn on when the offer is made in the particular flow — always map the sequence of communications rather than assuming a single model.

## What are common pitfalls?

- Treating price lists, advertisements, or shop displays as offers without checking the Boots/invitation-to-treat line of authority
- Assuming a counter-offer keeps the original offer alive
- Overlooking that revocation of an offer must ordinarily be communicated to the offeree before acceptance
- Applying the postal rule mechanically to instantaneous communications (email/instant message), where the better starting point is receipt/communication analysis

## When would a practitioner use this?

Useful when reconstructing whether a contract was formed from correspondence, RFQs, purchase orders, website checkouts, or oral exchanges, and when advising on whether negotiations are still pre-contractual.

## Quick reference

Offer = willingness to be bound on stated terms on acceptance. Invitation to treat (e.g. goods on shelf — Boots) is not an offer. Acceptance must be final and communicated; counter-offer kills the original offer (Hyde v Wrench). Battle of forms: often last shot (Butler Machine Tool). Unilateral offers: Carlill.

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*Reference material from [KTTC Legal](https://kttclegal.info/), not legal advice. Work product supports instructing solicitors and barristers under their supervision. England & Wales.*