What is the difference between a notification and a circular?
A notification is issued by a government (central/ state) to exercise the power of a legislative enactment (Parlimentary/ Assembly). These powers are in abundance in taxation (direct/ indirect) legislations. These notifications generally lay down the law taking care of some procedural aspects of the enactment. The circulars are issued by the chief executive in charge of the taxation hierarchy, and are normally explanatory/ interpretative or relax the rigours of the law administered.
AND IN OTHER WORDS....
circular is a internal memo or note of the Ministry/Department, which may clarify certain aspect of law. It may be superseded by yet another circular or legislative amendment. It has a persuasive value in judiciary, though the Courts are not bound by these. Any person having objection with a circular may approach the concerned Ministry/Department and seek alteration to that circular, which if fails, may challenge the same in the Courts. Ministry/Department issuing the circular are bound by their own circular. If they wish, they may withdraw or issue another circular to supersede the previous one.
A notification is a public notification in the Official Gazette and is issued in exercise of certain power derived from a legislative enactment or provision. It may relate to applicability of the legislations or any other variables. In several enactments, we see phrases such as "as may be prescribed". These are later notified through notifications. The Ministry/Departments are empowered to come out with notifications superseding the earlier ones. Notifications are integral part of the enactment and is binding on all the constituents.