according to G.K. Chesterton.
Any priggish pupil teacher could tell Dickens that there is no such phrase in English as “our mutual friend.” Any one could tell Dickens that “our mutual friend” means “our reciprocal friend,” and that “our reciprocal friend” means nothing. If he had only had all the solemn advantages of academic learning (the absence of which in him was lamented by the Quarterly Review), he would have known better. He would have known that the correct phrase for a man known to two people is “our common friend.” But if one calls one’s friend a common friend, even that phrase is open to misunderstanding.
From Appreciations and Criticisms of
the Works of Charles Dickens
Or, perhaps, Dickens wanted the idea of a common, meaning vulgar, friend to lurk behind his title. This would be especially true if he wanted to draw our attention a little away from the commonly assumed hero of the novel to, say, Boffin, who makes first use of the titular phrase in book I, chapter ix. Or maybe not.
Don’t think from this little bit of Chesterton’s essay that he disapproves of the title, or the novel. His point is more subtle, and his essay is worth the read.
An Addendum of Further Research: Perhaps, unknown to Chesterton, Dickens knew he was using “mutual” improperly, as he inserted the following on a slip of paper on the first page of the first serial and book editions of Our Mutual Friend: