What are the deferences between accounting theory and IAS?

One of the major differences is that the series of standards in the IAS were published by the International Accounting Standards Committee (IASC) between 1973 and 2001, whereas, the standards for the IFRS were published by the International Accounting Standards Board (IASB), starting from 2001. When the IASB was established in 2001, it was agreed to adopt all IAS standards, and name future standards as IFRS. One major implication worth noting, is that any principles within IFRS that may be contradictory, will definitely supersede those of the IAS. Basically, when contradictory standards are issued, older ones are usually disregarded.