Jackie, I believe, has hit on the answer. If Shelby is talking about what I think he is, it's words denoting a quality which, by its nature, does not admit of the comparative or superlative degree. One does not speak, except facetiously, of someone being very pregnant or very dead -- you're either pregnant or dead or you're not. Same goes for "the most pregnant" or "the deadest". Well, you might use 'dead' in a figurative sense, like "Smallburg is the deadest town I've ever spent time in" or something like that, but not in the literal sense.
Two of my favorite bugboos, which fall into this category, are 'unique' and 'perfect'. I don't care what those idiots say on QVC etc., something can't be very unique [shudder]. Something is either unique or it isn't; this is implied in the meaning of the word. Same goes for 'perfect' notwithstanding the preamble to the U.S. Constitution.
