The correct placing of "only" has been a matter of debate for more than 200 years. In 1762, Robert Lowth wrote: "The Adverb, as its name imports, is generally placed close or near to the word, which it modifies or affects, and its propriety and force depend on its position." He then contrasts the two sentences: "I only spake three words" and "I spake only three words". Fowler, writing in 1926, is particularly impatient when quoting one pedant who insisted on putting "only" next to the word it qualifies: "There speaks one of those friends from whom the English language may well pray to be saved, one of the modern precisians who have more zeal than discretion, and wish to restrain liberty as such, regardless of whether it is harmfully or harmlessly exercised." Fowler generally advises us to put "only" wherever we like, as long as we avoid confusion.
In the Longman Guide to English Usage, however (Penguin, 1996), Sidney Greenbaum and Janet Whitcut, who are generally on the liberal side of grammatical pedantry, advise: "In formal writing, `only' should come next to the word it qualifies." Consider, therefore, the different meanings of "Only John unveiled the slogan" (nobody else did); "John only unveiled the slogan" (he can't be held responsible for writing it); and "John unveiled only the slogan" (not the entire manifesto).
The question about only being safe with the Conservatives, therefore, comes down to two points: is it a formal, or informal statement; and is it sufficiently ambiguous to cause confusion?
When they say: "You're only safe with the Conservatives" do they mean you're not safe with anyone else? If this is what they mean, is there any chance that anyone encountering the phrase might take it literally to mean that you're only safe with the Conservatives? You're not well- off, you're not healthy, you're not educated with the Conservatives, but you are safe. If there is even a small chance that any voter could believe that, then they really ought to have put "only" in the right place.Reuse content