'To' and 'for the worse' - with an 'e' - have been used since the 15th century. With 'a turn', it just means a change to a condition which is less favourable. 'Worst' - with a 't' - would change it to least favourable, which does not really hang together with the idea of turning...ie just changing from one state to another.
Hi QM. I notice that in google for instance the Pope takes a turn for the worse and worst in news headlines before he dies. Should it be that when he first fell ill it was for the worse and when he was close to death it was for the worst?
Hello, Graeme. Personally, I would never use 'worst' in this situation, because it does not truly represent a ''turn'. The steady downhill progress of a terminal illness does not really involve 'turns'. However, were someone already on such a course, to experience a dramatic shift back towards wellness he might rationally be said to have experienced 'a turn for the better'.