Formation of a contract in Irish law follows the inherited common-law rules of offer and acceptance. The first question in almost every formation problem is whether a statement was a true offer (capable of being accepted) or merely an invitation to treat. Getting this wrong throws off everything that follows, because only an offer can be accepted to form a contract.
Advertisements are usually invitations to treat
An advertisement of goods for sale is normally an invitation to treat, not an offer — Partridge v Crittenden [1968] 2 All ER 421 Persuasive (Eng). The commercial logic is that a seller with limited stock cannot sensibly be treated as making a promise to the whole world that it will supply everyone who responds.
But this is a presumption, not a rule. Two well-known exceptions show an advert can be an offer where the wording shows a clear intention to be bound:
- Unilateral offers — a promise in return for an act. In Carlill v Carbolic Smoke Ball Co [1893] 1 QB 256 Persuasive (Eng) an advert promising £100 to anyone who used the product and still caught flu was an offer, because it evinced an intention to be bound (reinforced by a deposit lodged with a bank).
- "First come, first served" wording — an advert stating definite terms and quantity can be a firm offer, as in Lefkowitz v Great Minneapolis Surplus Store (1957) Persuasive (US), where a "first come, first served" advert was held sufficiently definite to be an offer.
Shop displays and price lists
Goods displayed in a shop window or on a shelf, and priced catalogues, are also invitations to treat. The customer makes the offer at the till, which the shop may accept or refuse — Fisher v Bell [1961] 1 QB 394 (flick-knife in a window) and Pharmaceutical Society of GB v Boots [1953] 1 QB 401 (self-service shelves) Persuasive (Eng). These English decisions state principles long applied in Irish law.
Why the distinction matters
It decides who can walk away and when. If a display were an offer, a shop would be bound to sell at a mispriced tag to everyone who "accepted." Because it is only an invitation to treat, the shop can decline. The distinction also fixes the moment of contract — and therefore who bears the risk if the price was wrong or the stock ran out.
The full, exam-ready version
Formation: offer, acceptance, the postal rule, revocation and certainty — with the full case table, worked problems and a model-answer skeleton. Checked against the primary sources.
or browse all modules →Frequently asked questions
Is an advertisement an offer or an invitation to treat?
Usually an invitation to treat (Partridge v Crittenden). But an advert can be an offer where it shows a clear intention to be bound — a unilateral promise (Carlill) or definite "first come, first served" terms (Lefkowitz).
Are goods in a shop window an offer?
No. A display is an invitation to treat; the customer makes the offer at the till, which the shop can accept or refuse (Fisher v Bell; Boots).
Why does offer vs invitation to treat matter?
Because only an offer can be accepted to form a contract. The distinction fixes the exact moment a contract is made and who is free to walk away before then.