Business entities carry on transactions of different nature. The types of transactions depend on the nature of business and the management policy. Many transactions may be of repetitive type, that is, similar nature of transactions take place repeatedly in a business entity. Therefore, transactions can be classified and grouped conveniently according to their nature. Generally, transactions are of two types: cash and non cash transactions (credit). Cash receipts and payments can be grouped in one category and credit transactions in another category. Thus, in practice, for easy, convenient, speedy and appropriate maintenance of accounts, the main journal may be sub-divided in such a way that a separate book is used for each category or group of transactions which are repetitive and sufficiently large in number. Each subdivision of the books is a special journal and a book of primary record or a book of primary entry or subsidiary book.
Journal entries are not passed when records are made in subsidiary books. When journal is the only book of prime entry it is possible for only one book-keeper to enter transaction in it at a time. In case of business entities having large volume of transactions, one person cannot do all the recording work by himself. There is a need for sub-division of the book-keeping work leading to the sub-division of the journal into parts or subsidiary journals.