While I sort of see what you're getting at, it's not entirely clear what the difference between these 2 is. How is the former (a 'reasonable' language) all that

While I sort of see what you're getting at, it's not entirely clear what the difference between these 2 is. How is the former (a 'reasonable' language) all that different from the latter (a 'useful' language)? While reasonableness and usefulness are not the same thing, it does seem a language needs to be both. Otherwise you could end up with a language that is both useful and unreasonable, which would be maddening.