Absolute Adjectives

Some adjectives, including superlative adjectives like last and best, along with other adjectives like full, pregnant, perfect, the word absolute itself, and unique (which literally means “one of a kind”), technically should not be modified by intensifiers like very and extremely or qualifiers like somewhat and a little because they indicate qualities of an absolute degree. A woman is either pregnant or not pregnant, for example; she can’t be “a little pregnant.”

the very best performance
the best performance

a very perfect performance
a perfect performance

a rather perfect performance
an excellent performance

In practice, however, this rule is often disregarded. It may make sense to describe a woman as “very pregnant,” for example, if you mean that her pregnancy is advanced and her stomach is quite large. (Unique, in particular, is often modified by an intensifier. Many people think of uniqueness as a quality that can have different degrees; one person, for example, can be “more unique” than another person.)