Outwardly, the bond of a common language and common liturgy is often the essential and radical division of a schism.
Indeed these Eastern Catholic bodies in many cases still faintly reflect the divisions of their schismatical relations.
The point may be stated more scientifically by using the old division of the patriarchates. Western Christendom may be defined quite simply as the Roman patriarchate and all Churches that have broken away from it.
All the others, with schismatical bodies formed from them, make up the Eastern half.
Historically and archeologically, it is a secondary question.
Each Catholic body has been formed from one of the schismatical ones; their organizations are comparatively late, dating in most cases from the sixteenth and seventeenth centuries.
An accident of political development has made it possible to divide the Christian world, in the first place, into two great halves, Eastern and Western.
The root of this division is, roughly and broadly speaking, the division of the Roman Empire made first by Diocletian (284-305), and again by the sons of Theodosius I (Arcadius in the East, 395-408; and Honorius in the West, 395-423), then finally made permanent by the establishment of a rival empire in the West (Charlemagne, 800).
Their adherents everywhere belong of course to the Western portion.
It is now possible to draw up the list of bodies that answer to our definition.
We have already noted that they are by no means all in communion with each other, nor have they any common basis of language, rite or faith.
All are covered by a division into the great , those formed by the Nestorian and Monophysite heresies (the original Monothelites are now all Eastern-Rite Catholics), and lastly the Catholic Eastern Rites corresponding in each case to a schismatical body.
The Nestorian heresy left a permanent Nestorian Church, the Monophysite and Monothelite quarrels made several more, the reunion with Rome of fractions of every Rite further increased the number, and quite lately the Bulgarian schism has created yet another; indeed it seems as if two more, in Cyprus and Syria, are being formed at the present moment (1908).