Colwell's rule

Colwell's rule states 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....”

It means that if you have decided beforehand from context and other indications that a noun is definite and a predicate nominative and is before the linking verb, then the chances are high that it does not have the article. Some internet resources say the chances are 80% it does not have an article but I can't find the references to support this.

Note also that the rule does not apply in reverse: if you see a predicate nominative and it is before the linking verb, the chances are high that it is definite. Wallace states that this is how Colwell's rule has often been wrongly applied in respect of John 1:1c to assert that θεὸς must be seen as definite. In fact this is applying the reverse of Colwell's rule.

Wallace gives the analogy: if one sees rain, chances are high that there will be clouds. But this does not mean that if one sees clouds, chances are high that there will be rain. Wallace also quotes Harner's analysis which shows that 80% of the time predicate nominatives before the linking verb are qualitative, 20% definite (and so only rarely indefinite). Wallace thus argues that θεὸς in John 1:1c be seen as qualitative, that is, the Word was equated to the God-attributes. To assert θεὸς as indefinite is rare by Colwell's rule, and would be Arianism. But to assert that θεὸς is definite could be seen as Sabellianism.