Catholics are not Orthodox because they caused a schism by changing the Apostolic Faith. The early Church was Conciliar in Nature, it was ruled by the Ecumenical Councils for matters of heresy and by the local councils of bishops for all other matters. These councils never taught that the Holy Spirit proceeds from the Son, they only taught that he proceeds from the Father. A local council of Toledo, Spain arround the year 500 added the the phrase "and of the Son" to the Nicene Creed which reads "The Holy Spirit Proceeds from the Father.." This change was resisted by all of the Patriarchs, Rome included. Rome did not give in to this change until Charlemagne forced the Pope to accept this change under the threat of violence. There is also a big difference in the way the Catholics view original sin and the way Orthodox do. This difference in teaching has led to all kinds of other differences which have sprung up in the West in order to explain the Catholic view of original sin. Finally, Catholics are not Orthodox because they reject the counciliar nature of the Church and teach the Patriarch of Rome has Primacy of Jurisdiction, Universal Jurisdiction and is Infallible. These are the three major differences between Orthodoxy and the Roman Catholic Church. It is for these reasons there is a schism between the Churches. We call ourselves Orthodox Christians because orthodox means correct teaching. Rome can not be Orthodox because it teaches incorrectly, ie. it has added to the Apostolic faith.