(i) A condition is a stipulation which is essential to the main purpose of the contract. It is core to the contract.
(ii) The non-fulfillment of the condition cancels the very contract.
(iii) E.g. 'A' intends to buy a motorbike from 'B. 'A' insists that the bike should give him a mileage of 50 km per litter.
(iv) He prefers to have a red color bike. 'B' a mechanic gets a bike which gives him 55 kms per litter.
(v) But the color is green. In this case, 'A' cannot cancel the contract.
(vi) Since 'A'. is very particular about the mileage, it is a condition to the contract.
(vii) That part of the contract is fulfilled by 'B'. However, 'A' can ask the mechanic 'B' to bear the cost of repainting it with red color.

(i) Transfer of property (ownership) in goods from the seller to the buyer is the main object of a contract of sale.
(ii) The term property in goods must be distinguished from possession of goods.
(iii) Property in goods means the ownership of goods while possession of goods refers to the custody of goods or control over the goods.
(iv) For eg. 'A'  may possess a watch. Just because 'A' possesses the watch, he cannot be owner. He might have borrowed the watch from his friend or stolen the watch from somebody or found it on the highways. In this case, he cannot be called owner.

(i) Specific Goods: 
Specific goods denote goods identified and agreed upon at the time of contract of sale. For eg, if a buyer selects a particular variety of saree after examining several other sarees, the selected one denotes specific goods.
(ii) Ascertained Goods:
The term ascertained goods is also used as similar in meaning to specific goods. But this term may even refer to goods which become ascertained subsequent to the formation of the contract.
(iii) Unascertained or Generic Goods:
These are goods which are not identified and agreed upon at the time of contract of sale. For eg, A wants to buy a car from a showroom where different models at different prices have been displayed. All these displayed models represent unascertained goods.

In every contract of sale, there are certain expressed and implied conditions and
warranties.
The term implied conditions means conditions which can be inferred fromn or guessed from the context of the contract.

Following are the implied conditions :
(i) Conditions as to Title.
(ii) Conditions as to Description.
(iii) Sale by Sample.
(iv) Conditions as to Quality or Fitness.
(v) Conditions as to Merchantability
(vi) Condition as to Wholesomeness.
(vii) Condition implied by Trade Usage.
Following are the implied warranties :
(i) Quiet Possession.
(ii) Free from Any Encumbrances.
(iii) Warranty in the case of Dangerous Goods.

Existing goods are those owned or possessed by the seller at the time of contract of sale. Goods possessed even refer to sale by agents or by pledgers. The existing goods may be either :
(i) Specific Goods : Specific goods denote goods identified and agreed upon at the time of contract of sale.
(ii) Ascertained Goods: The term 'ascertained goods' is also used as similar in meaning to specific goods.
(iii) Unascertained or Generic Goods: These are goods which are not identified and agreed upon at the time of contract of sale.

Rights of an Unpaid Seller against the Goods
(1) Right of Lien: 
An unpaid seller has a right to retain the goods till he receives the price. But to exercise this lien
(i) He must be in possession of goods
(ii) The goods must have been sold without any stipulation as to credit or where goods have been sold on credit, the terms of credit must have expired.
(iii) It must be remembered that the right of lien depends on actual possession of goods
Where the Property in the Goods has Passed to the Buyer.
(2) Right of Stoppage in Transit: 
Where the seller has delivered the goods to a carrier or other bailee for the purpose of transmission to the buyer, but the buyer has not acquired them, then the seller can stop the goods and regain the possession. 
(3) Right of Resale:
The unpaid seller can resell the goods
(i) Where they are of a perishable nature or
(ii) After exercising his right of lien or stoppage in transit, even though he has given intimation to the buyer of his intention to resell, buyer has not tendered the price within a reasonable time.
(iii) Where the seller has expressly reserved the right of resale in the contract itself.

(1) Existing Goods
(i) Specific Goods - Specific goods denote goods identified and agreed upon at the time of contract of sale.
(ii) Ascertained Goods - (a) The term ascertained goods is also used as similar in meaning to specific goods.
(b) But this term may even refer to goods which become ascertained subsequent to the formation of the contract.
(iii) Unascertained or Generic Goods - These are goods which are not identified and agreed upon at the time of contract of sale.
(2) Future Goods
These are goods which a seller does not possess at the time of contract of sale but which will be manufactured or produced or acquired by him after entering into the contract of sale agreement
(3) Contingent Goods
Contingent goods are the goods, the acquisition of which by the seller depends upon a contingency (an event which may or may not happen). Contingent goods are a part of future goods.

Following essential elements are necessary for a contract of sale
(i) Two Parties :
(1) A contract of sale involves two parties - the seller and the buyer.
(2) The buyer and the seller should be two different persons. If a person buys his own goods, there is no sale.
(ii) Transfer of Property :
(1) To constitute sale, the seller must transfer or agree to transfer the ownership in the good to the buyer.
(2) A mere transfer of possession does not amount to sale.
(iii) Goods :
(1) The subject matter of contract of sale must be goods. It excludes money, actionable claims and immovable property.
(2) The term 'goods' includes every kind of movable property, stocks and shares, growing crops etc.
(3) Goodwill, trademarks, copy rights, patent rights etc., are all also regarded as goods.
(iv) Price :
(1) The monetary consideration for the goods sold is called price.
(2) If goods are exchanged for goods, it is only barter and not a sale.
(3) But if goodsare sold partly for goods and partly for money, the contract is one of sale.
(v) Includes both 'Sale' and 'Agreement to Sell' :
(1) The term contract of sale includes both sale and agreement to sell.
(2) If the property in goods is transferred immediately to the buyer it is called a sale.
(3) On the other hand, if the transfer of property takes place at a future date or on fulfillment of certain conditions, it is called 'an agreement to sell'.