Offer
The first and foremost essential element of a valid contract is offer or proposal. Section 2 (a) of ICA defines Proposal as:
When one person signifies to another his willingness to do or to abstain from doing anything, with a view to obtain the assent of that other to such act or abstinence, he is said to make a proposal.

Elements Of A Proposal
i. Expression of willingness to do or not to do something;
ii. Made to another person;
iii. With a view to obtain the assent of that other person.

Carlill v. Carbolic Smoke Ball Co.,1 QB 256
• The Carbolic Smoke Ball Company, once advertised that their Carbolic Smoke Ball was a cure of several diseases including flu, bronchitis, cough, cold etc. 
• The company was so confident that it published in the advertisement that any person who would use the smoke ball thrice a day, for two weeks according to the printed directions and still catches Influenza would be eligible to claim 100 pounds from the company.
• Mrs. Carlill, the plaintiff used the smoke ball as per the printed directions but still caught influenza and claimed for the money from the company which the company denied.
• The defendant in its argument submitted that the advertisement was merely a sale puff and can’t be considered as an offer as offer can’t be made to the world.

It was held that, the advertisement was not a unilateral offer to the whole world, but an offer restricted to those who acted upon the terms contained in the advertisement. Thus, the plaintiff was purely entitled to the claim of 100 pounds.

Essentials Of A Valid Offer
i. It must be certain, definite and not vague.
ii. Must be communicated to the offeree by the offerer. 
iii. May be conditional (but not against public policies).
iv. Must be capable of creating legal relationship.
v. Should not contain any undue terms.

Types Of Offers
An offer can be of many types, and ranging from the vast pool of Contract, the following are the six basic kinds of offer:
• Express offer
• Implied offer
• General offer
• Specific offer
• Cross offer
• Counter offer

Express Offer
Section 9 of ICA says: In so far as the proposal or acceptance of any promise is made in words, the promise is said to be express.
Thus, any offer which is made by words (either spoken or written) is considered as an express offer.

Implied Offer
Section 9 of ICA also says that: In so far as such a proposal or acceptance is made otherwise than in words, the promise is said to be implied.
Therefore, any offer or set of offers made through any mode other than written or verbal words is considered as implied offer. It may include (i) offer through conduct of the parties, or (ii) offer through the circumstances.

General Offer
The offer which is made out to the world at large is called a general offer. The idea of general offer was given to the world post the Carbolic Smoke Ball Co. case, stating the theory that, performance of the condition is sufficient acceptance without ratification.

Section 8 of the ICA talks about performance of conditions for fulfilment of a contract: Performance of the conditions of a proposal, or the acceptance of any consideration for a reciprocal promise which may be offered with a proposal, is an acceptance of the proposal.

This means that in cases of general offers, there is no need of communicating the acceptance and the performance of the condition would clearly imply about the acceptance of the offer.

Specific Offer
The offer which is made to a particular or ascertained person or group of persons and the acceptance of the same can be given by that specific party(s) only is called a specific offer. 
Boulton v. Jones
(1857) 2 H and N 564
• The plaintiff had taken over the business of one, Brocklehurst with whom the defendant had old business relations.
• The defendant not knowing about the change in ownership, sent him a requirement of certain goods.
• The defendant later on after receiving an invoice by the plaintiff, at that point came to know about the change in ownership, and by then he had already consumed the goods.
• The defendant refused to pay as he already had a settlement with the previous owner for the same. The plaintiff sued him for non payment of the money.
It was held that the defendant was not liable to pay any penny. It clarified that if one wants to contract with 'A' then 'B' can’t substitute 'A' without the knowledge of the other party. It also held that whenever someone comes into contract with a specific party, no other person can come out and say that he is the party contracted with.

Cross Offer
When there are identical offers made by two parties to each other without the knowledge of each other’s offers, cross offer is said to be created and since there is no acceptance of any such offer, cross offers are not considered valid.
For example, 'A' makes an offer to 'B' to sell his car for 10 Lakhs and 'B' in absence of knowledge of the same, makes an offer to 'A' to buy his car for 10 Lakhs and thus, there is no acceptance of such an offer. This is called cross offer.
It must be noted that for constituting a valid contract, there should be am offer made and the same be accepted, but since in a cross offer there is no such acceptance but, only simultaneous offers, therefore, a cross offer will never lead to the formation of a valid contract.

Counter Offer
When a previous offer is accepted by the offeree but with some changes and valid modifications, then such an offer is said to be a counter offer. Thus, a counter offer is the rejection of an old offer and a new offer is placed instead.

For example, if 'A' offers 'B' to sell his car for 5 Lakhs and 'B' agrees to buy it for 3 Lakhs only, to which 'A' agrees. Here, the old offer is rejected and a new offer is placed. This offer will be called a counter offer.

Communication Of Offer
Communication of the offer is the most essential condition to be fulfilled for creation of a valid contract. An offer is valid if it is communicated to the offeree. As discussed, the communication may be either expressed or implied. 

Section 4 of ICA says that, the communication of a proposal is complete when it comes to the knowledge of the person to whom it is made.
Lalman Shukla v. Gauri Dutt (1913) 40 All 489

• The plaintiff was the servant of the defendant to whom his master had asked to find his missing nephew.
• Meanwhile, the defendant announced a reward of 501 Rupees for anyone finding his nephew of which, the servant wasn’t aware.
• Later on, when the servant brought his master’s missing nephew, he claimed for the said reward to which the master simply denied.
• The plaintiff sued his master arguing that, mere performance of the act was sufficient to entitle a person performing it to claim the reward advertised for.
• The defendant in his defence contended that since there was no communication of the offer to the plaintiff, thus, it doesn’t create any valid contract.
It was held by the Allahabad High Court that, although the performance of the condition was there on the part of the plaintiff still it won’t create any contract, since, the knowledge of the offer was missing to the plaintiff. Thus, the right of reward was dismissed as it could only be founded upon a contract.

Revocation Of Offer
Section 5 of the ICA says that, the offer may be revoked anytime before the communication of the acceptance is complete against the proposer/offerer.
Acceptance as against the proposer means that, when the acceptance is put in the course of transmission, so as to be out of the power of the acceptor to withdraw the same.
This means that once an offer is made and is accepted by the offeree, the offer can’t be revoked. Withdrawal of the offer can only happen before the acceptance of the same by the offeree.

Invitation To Offer
An invitation to offer which is also sometimes called as invitation to treat is an offer which is made to the seller and not made by the seller. An invitation to offer as understood from the term is calling parties to offer something. As per this, initially, there is no such pure intention of any party to enter into a contract. Thus, we can say that it is the offer which the buyer makes to the seller and to which, the seller has a complete right to whether accepting or letting it go. The seller without any dispute, will only accept that offer whichever he finds best for himself.

Illustration
If 'A' displays a certain kind of alcohol at his liquor shop, but intends to sell it only to people who he wants. Here, the displayed alcohol is an invitation to offer and only becomes an offer when the buyer accepts the invitation and makes an offer.

This type of contractual system can be observed mostly at the malls, shops and food outlets around us.