The methods of textual criticism may be broadly described as two in number- the comparison of documentary evidence, and conjecture. The two methods are mutually complementary. Where documentary evidence is plentiful, conjecture will be scarce; but where the former is wanting, the latter will have to try to take its place to the best of its ability. In the case of the New Testament the documentary evidence is so full that conjecture is almost excluded, and it is with the principles of the interpretation of documentary evidence that we are most concerned here. Some statement of these is necessary, as an introduction to a summary of the evidence itself.
- from page 7, Handbook to the Textual Criticism of the New Testament