4. Sale of Goods Act, 1930

CONTRACT OF SALE
Section 4(1) of the Sale of Goods Act, 1930 defines the term as - 'Contract of Sale' as - a contract of sale of goods is  a contract whereby the seller transfers or agrees to transfer the property in goods to the buyer for a price. 

ESSENTIALS OF A CONTRACT OF SALE
1. Two Parties
2. Subject matter of the contract must necessarily be goods.
3. A price in money(not in kind) should be paid or promised.
4. A transfer of property in goods from seller to buyer must take place.
5. A contract of Sale must be absolute or conditional[sec4(2)]
6. All other essentials of a valid contract must be present

AGREEMENT TO SELL
Section 4(3) of the Sale of Goods Act, 1930 the term- ' where under a contract of Sale the transfer of the property in the goods is to take place at a future time or subject to some condititon thereafter to be fulfilled, the contract is called an Agreement to Sell. 

HIRE PURCHASE
Hire Purchase is paying installments with the intention of owning the goods after paying the last installment. The goods passes on to the hirer upon payment of the last installment. 
In case of non payment of installments by the buyer, Seller has the right to
- retain the goods
- retain the installment money (and treat it as hire charges)


CONDITIONS
Sec 12(2) defines Conditions as a stipulation essential to the main purpose of a contract, the breach of which, gives right to treat the contract as repudiated.

 WARRANTIES
Sec 12(3) defines   Warranty as a stipulation collateral to the main purpose of a contract, the breach of which, gives right to claim for damages but no right to reject the goods & treat the contract as repudiated.