What Makes a Valid Contract?
Offer and Acceptance
To prove that a contract is valid there must be facts identifiable as an offer and as the acceptance of that offer.
A mere ongoing relationship of trust and cooperation is not going to qualify as a contract. There needs to be a definite commencement to the contractual aspect to the relationship with the recognition of rights and obligations evident. This is especially important when enforcing contracts implied by conduct. A meeting of minds is necessary where parties’ intentions mirror each other...
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The Postal Rule
Where an offeror issues an offer to be accepted by post, the date of the acceptance is the date on which the offeree sent their acceptance. If the offeror sent a further letter revoking the offer, this is dated by when the offeree received it. The same principle will apply to modern electronic communications of all sorts.
 Empirnall Holdings Pty Ltd v Machon Paull Partners Pty Ltd (1988) 14 NSWLR 523.