Sale has been defined in the article 338 of civil code as :"sale is passing (the) original thing to known consideration". This definition that is adopted from the sale definition by some Imamyh jurists indicates that the contract of  sale is possessory and apparently is in contrast with the presented definition in the article 183 of civil code ,because from the said article the obligatory nature of the contracts can be inferred not the possessory being of them .Among the other subjects that can be examined and put forward by considering article 338 is the sale of the unascertained goods .This subject is also put forward about choses in action such as the rights of authors ,inventors ,and key money .At any rate ,these two cases require separate examining that whether they are regarded as sale or not?

Another subject that is related to sale's subject is consideration by noticing this fact that consideration ,upon custom and usage ,is in the form of money at the present time .The matter in hand is this fact that if consideration be non-cash (or in kind)and be one of the properties (of the said person),can it be regarded as sale or it should be treated as contract of barter ,hiring of persons ,hire-purchase , gift with consideration that sometimes put forward some difficulties in recognizing the legal nature of the performed action .This case requires to determine the clear and  precise principles and the inclusive and exclusive criteria for distinguishing sale from such similar contracts .The practical results of this distinction is in the difference between laws and resulting effects on these legal institutions .

On the basis of what has been mentioned above ,it is important to express the contract of sale as the mother of contracts in the Iranian Law and to represent inclusive and exclusive criteria for distinguishing  it from the other contracts and to examine subject comparatively in the British Law ( in order) to clarify weak and strong points of domestic law and also to fill the existing legal gaps or to amend legal articles .