If you are comparing only 2 things, should you use the comparative (eg bigger) or the superlative (eg biggest)? Style guides tend to advise us to use the comparative. But I came across a case where the comparative could be ambiguous.
Suppose you are writing about 3 brothers from the perspective of the youngest. You want to say that he is playing with the oldest of the 3. The sentence He is playing with his older brother is ambiguous: both his brothers are older than him.
You could remove the ambiguity by saying He is playing with the older of his 2 brothers. That sounds rather stilted. Or you could just say He is playing with his oldest brother. That sounds more natural, but grammatical pedants might object that the youngest one has only 2 brothers.
In comparing 2 items, is the superlative really so bad?
You often hear or see the superlative used in comparing 2 items, even though style guides often criticise this usage. No doubt, this usage would be even more common if style guides and teachers didn’t try to stamp it out.
Style guides tend to argue that it is ‘illogical’ to use the superlative in comparing only 2 things. I’m not sure, though, that it is really illogical. The bigger of 2 things is also the biggest of those 2 things.
So, although the superlative may be unnecessary in that case, I don’t see anything logically wrong in using it then. Indeed, the prevalence of this usage suggests that natural English does permit the superlative in this case and that the style guides’ ‘logical’ rule is artificial.
In formal writing and very formal speech it is probably best to stick to the style guides’ artificial rule—though taking care to avoid ambiguity. On the other hand, in less formal settings, I see nothing wrong with using the superlative.