In Guy de Maupassant’s short story ‘Le Horla’, which I read in The Mountain Inn and other stories (Penguin Classics, 1955; translated by H. N. P. Sloman), I came across a restrictive clause using which and set off by a comma:
I had an experience
todayyesterday, which has upset me considerably.
Lest there be any doubt: the context indicates it was the particular experience the narrator had that upset him, not the fact of his having any old experience. The normal approach in such cases is to forgo the comma and use either which or that: I had an experience today which has upset me considerably.
I wonder at what point – and from whose hand – the comma appeared. Was it meant simply to signal a slight pause, its grammatical ambiguity an accident of shifting styles? Or was it inserted needlessly by an editor schooled in the fake that/which rule? Either way, it bears comparison with this rogue comma in a recent Guardian editorial.