(Sixth post in a series; understanding this post may require reading the others first.)
In the last post, I shared that most modern English translations begin with one of two Greek New Testaments. The first is the Textus Receptus, first published by Erasmus of Rotterdam in 1518. At that point in history, Erasmus had available to him six Greek manuscripts from which to make his decisions about what the original New Testament books contained. Each of the six was representative of an essentially Byzantine text type, and each would have dated from no earlier than the ninth century AD.
A couple of things are important to note here. First, the Textus Receptus is an excellent Greek New Testament, and basing a modern translation on it remains a valid option.
Second, the Textus Receptus and the Byzantine text tradition are not the same thing. There existed variants even within those six manuscripts, and Erasmus would also have had at his disposal a number of early translations (especially in the Latin) and the quotations from several early church fathers with which to compare them as well. Thus, he undoubtedly made decisions much like those made by textual critics today, deciding among variants on the basis of both external evidence and internal evidence.
External evidence is that involving the manuscripts themselves. The two main principles regarding external evidence are 1) prefer the oldest reading and 2) prefer the most widespread reading. As we will see (in the next post), Erasmus did not have as much external evidence (as many manuscripts, translations, and writings of church fathers) as is available today.
Internal evidence refers to issues regarding what type of "error" occurred. Several principles are used, things like "prefer the shortest reading" (though this is not always appropriate) and "prefer the more difficult reading." But all of these principles can be more or less subsumed by or summarized under the principle "prefer the reading that best explains how the other variant(s) arose."
The primary English translations in use today that are based on the Textus Receptus are the King James Version and the New King James Version.