If you’ve ever heard a Jehovah’s Witness (or anyone else) translate John 1:1c as “and the Word was a god” (like the NWT translation) then you need to read this. Note: you don’t have to know Greek to read and understand this essay, but it would help. :-)
Definition of Colwell’s Rule
Colwell’s Rule pertains to a specific grammatical construction in the Greek New Testament: anarthrous pre-verbal predicate nominatives that are judged to be clearly definite in context. Wallace begins by clarifying the terms.
- Anarthrous = without the article
- Pre-verbal = before the equative verb
- Predicate nominative (PN) = the noun in the nominative case which is the same as the subject (more or less).
This specific construction was the limited field of investigation that led to the discovery of Colwell’s Rule. While first studying John 1:49 (and then other verses with definite PNs in similar grammatical constructions), Ernest Cadman Colwell discovered that “Definite predicate nouns which precede the verb usually lack the article…a predicate nominative which precedes the verb cannot be translated as an indefinite or a ‘qualitative’ noun solely because of the absence of the article; if the context suggests that the predicate is definite, it should be translated as a definite noun…” Colwell noted that in John 1:49 (apekrithē autō Nathanaēl, Rabbi, su ei ho huios tou theou, su basileus ei tou Israēl [Nathanael answered to him, “Rabbi, you are the Son of God, you are the king of Israel”]), while the two PN constructions differed according to the presence of the article and the word order of the PNs, the meanings were similar. Colwell then made the assumption that the definiteness of a PN could be defined from a shift in the word order. His discovery was first published in 1933 as an article entitled, “A Definite Rule for the Use of the Article in the Greek New Testament,” in JBL 52 (1933) 12-21. This well-known article has since led to the particular rule being named Colwell’s Rule, summarized as “a PN that precedes the copula [i.e., the equative verb], and which is apparently definite from the context, usually lacks the article.”
Continue reading here.
 The three definitions following are from Daniel B. Wallace, Greek Grammar Beyond the Basics: An Exegetical Syntax of the New Testament (Grand Rapids: Zondervan, 1996), 256.
 Wallace, GGBB, 257. He cites Colwell, “A Definite Rule for the Use of the Arti¬cle in the Greek New Testament,” in JBL 52 (1933), 20.
 Wallace, GGBB, 257. Italics original.