The Metropolitan Police have put up big posters on the Underground telling people what to do if they see a bag without an owner. ‘Don’t touch, check with other passengers, inform station staff or call 999,’ it says. You might think that I am being captious in thinking this reads badly. If the word don’t governs all the subsequent imperatives, then the doubting passenger ends up doing nothing. The ambiguity is not helped by the conjunction or. The Met’s message in conventional prose would have the first two words as a separate sentence: ‘Don’t touch. Check with other passengers, inform station staff or call 999.’ (I don’t much care for the Americanism call. If someone says ‘I’ll call tomorrow,’ I sometimes think they intend to come round to the house. The English is phone. But never mind.) The advertising people went against fashion in putting all those clauses in one sentence, when the tendency is the opposite. You know. Sentences without verbs. Disjointed. Like Tony Blair’s speeches. Annoying. Sometimes.
There is more of a problem in defining a sentence than we might suppose. Certainly it was good to be taught as little children that a sentence should have a verb. Ordinarily we might expect a subject too. Henry Fowler in Modern English Usage (1926) wrote, ‘Sentence, in grammar, means a set of words complete in itself, having either expressed or understood in it a subject and a predicate, and conveying a statement or question or command or exclamation.’
‘Don’t touch’ would be for Fowler an elliptical sentence, since its subject is not expressed nor is any predicate. Interestingly, Fowler regards as two sentences an example like, ‘You commanded and I obeyed.’ Another thing we were probably taught is that a sentence should not begin with and. But then we discovered that in the admired prose of the King James Bible, sentence after sentence begins with and. As for verbless sentences, much depends on context. They are often used in dialogue. In response to questions, an answer may simply be ‘Yes’ or ‘No’, words which perform a grammatical function that had to be expressed less neatly in Latin. But the answer might well be ‘Blue’ or ‘Hot’. Moreover, prose that resembles oral speech, either as dialogue or as monologue, even distantly, is often improved by the use of verbless sentences. Here is a random bit from Elizabeth Longford: ‘This was the kind of woman Queen Victoria truly admired: one with spirit who was also kind to the servants. “High tone” without “John Bullism”.’ Indeed.