Page:The king's English (IA kingsenglish00fowlrich).pdf/257

(Commenting) The Thames, which runs through London, is turbid.

It will be seen that in the first the relative clause is an answer to the imaginary question, 'Which river?'; that is, it defines the noun to which it belongs. In the second, such a question as 'Which Thames?' is hardly conceivable; the relative clause gives us a piece of extra and non-essential information, an independent comment. The two types are not always so easily distinguished as in these examples constructed for the purpose. What we wish here to say is that it would contribute much to clearness of style if writers would always make up their minds whether they intend a definition or a comment, and would invariably use no commas with a defining clause, and two commas with a non-defining. All the examples that follow are in our opinion wrong. The first three are of defining relative clauses wrongly preceded by commas; the second three of commenting relative clauses wrongly not preceded by commas. The last of all there may be a doubt about. If the long clause beginning with which is intended merely to show how great the weariness is, and which is practically equivalent to so great that, it may be called a defining clause, and the omission of the comma is right. But if the which really acts as a mere connexion to introduce a new fact that the correspondent wishes to record, the clause is non-defining, and the comma ought according to our rule to be inserted before it.