To have an agreement, you must first have a valid offer.An offer can be made in writing, verbally or by conductThe rules of an offer are as follows The offer must be communicated by the offeror (which is the person making the offer) to the offeree (which is the person receiving the offer) Taylor v Laird  25 LJ EX 329 An offer can be withdrawn before acceptance Routledge v Grant  4 Bing 653 An offer can be made to the whole worldCarlill v Carbolic Smoke Ball co  1 QB 256The terms of the offer must be certain Guthing v Lynn  2 B & AD 232
Goods displayed in a shop windowFisher v Bell  1 QB 394 Advertisements in Newspapers or a magazine are also invitations to treat, there is no contract in place until one party makes the offer to buy, which then needs to be accepted.Partridge V Crittenden  1 WLR 1204 Goods displayed on a shelfPharmaceutical Society of GB V Boots Cash Chemist Ltd  1 ALL ER 482 Mere statement of price
Advertisements which state a promise such of that in:Carlill V Carbolic Smoke Ball LTD  1 QB 256This is not an invitation to treat because of the promise stated on the poster. The promise forms the offer.
An offer can be accepted verbally, in writing or by conduct Acceptance must be the mirror image of the offer.Hyde V Wrench 49 ER 132 Acceptance must be communicatedPowell V Lee  99 LT 284 Silence is not considered acceptanceFelthouse V Bindley  142 ER 1037
Acceptance has taken place one the letter has been postedAdams V Lindsall  106 ER 250 Even if the letter is lost or destroyed Household Fire Insurance Co V Grant 
Consideration is defined as the price of which the promise of the other is bought Consideration doesnt have to be adequateThomas V Thomas 2 QB 851But it must be real and have actual valueChappell & Co Ltd V Nestle & Co Ltd  AC 87 Consideration may be executionary but not pastRoscorla v Thomas 
Two presumptions Social and Domestic Arrangements Commercial Arrangements
Usually not legally bindingBalfour v Balfour  2 KB 571Unless the couple are estrangedMerritt V Merritt  1 WLR 1211
Usually legally bindingEdward V Skyways Ltd  1 WR 349UnlessThe intention not to be legally bound is made in agreementJones V Vernon Pools Ltd  2 ALL ER 626
Bob, who is a butcher has put a poster up in his shop window We need to work out if this is an offer? Or an invitation to treat? Is there a contract –Is there a offer and acceptance? Is there consideration and is there intention to create legal relations.
If the poster had stated a unilateral promise as that inCarlill V Carbolic Smoke Ball LTD  1 QB 256 Bobs poster would be a valid offer, which the customer could accept BUT the acceptance doesn’t mirror the offer Therefore, there is no contract in place – so the customer can’t sue Bob for breach of contract
If this was a Social or domestic agreement it is presumed not to be legally bound – there for No contractLens v Devonshire Club (1914) But commercial arrangements are presumed to be legally binding, so Bob would be liable for breach of contract. Peter would be able to claim reliance loss for the work Bob did not complete Anglia Television Ltd v Reed  1 QB 60