I was talking with my friends the other day about what is heathy to eat, I brought up the fact that something can be healthy if you compare it to something that is not healthy. You could say a doughnut is healthy if you compare it to bacon but you can say a doughnut is very unhealthy if you compare it to a salad. Likewise, I could say that I'm tall, but in comparison to my house I'm not very tall at all. Are all adjectives comparative?
No. Many can't be, for a number of reasons. A brief summary from here:
There's syntax and then there's semantics.
Syntactically, superlatives, like 'most interesting' or 'tallest', are adjectives that grammatically cannot be used to from superlatives. That is
is not syntactically allowed. Also it doesn't make much sense; logically how can something be taller than the tallest?
For most other adjectives, one can form, according to the rules of English grammar, superlatives. But semantically there can be problems. There's the old chestnut
because most saliently one is either pregnant or not. So semantically
should be logically impossible. However, most words and concepts (outside of mathematics) allow range of application and vagueness and metaphor. One can be further along in a pregnancy, more American, deader than a door nail. So comparative formation is more productive than one would expect logically.