As mentioned above, the liturgy for the Eucharist is important in Anglican eucharistic theology because of the principle of "lex orandi, lex credendi". The liturgy is defined in the authorised prayer books of the various national churches and ecclesiastical provinces of the communion. The eucharistic rites follow one or other of two main sources, either the First English Prayer Book of 1549 or the Second of 1552 which, with minor modifications, became the 1662 Book BCP which is still today the official and legal reference-point for the Church of England. The author of both rites was Thomas Cranmer, who maintained that there was no theological difference between the two, but was forced to make its reformed theology more obvious when conservative clergy hostile to the English Reformation took advantage of loopholes in the 1549 prayer book to make the new liturgy as much like the old Latin Mass as possible, including elevating the Eucharist.