In a recent question about comparatives, a dispute arose in the comments about gradable antonyms like useful/useless where English speakers strongly prefer to use comparative forms only for half of the pair.
I proposed that this is simply an example of marked word pairs, a kind of asymmetry where one word of a pair is the dominant or default form for general use. Marking explains why we normally ask, “How old are you?” instead of how young. I think it also explains why it sounds awkward to say, “This is more useless than that,” unless we add emphasis: “This is even more useless than that.”
Edwin Ashworth disagrees, claming: “Useful is not an absolute adjective, whereas useless is. The opposite of useless is possibly essential.” I take this to mean that useless properly has a complementary antonym like on/off or day/night, where the two meanings don't lie on a spectrum and don't normally permit comparatives. But essential and useless still form a gradable spectrum, and phrases like more essential are not at all uncommon. I doubt that it's even possible to find a complementary antonym for useless, as utility is inherently gradable.
However, another possibility occurred to me: Is there a class of half-graded antonyms, where the two meanings lie on a spectrum, but only one of the words is gradable, while the other is absolute? This would work like a dimmer switch, where instead of on/off, you have something more like bright/off. One such antonym might be doubtful/doubtless: Wiktionary lists the adjective form of doubtless as not comparable.
My intuition is that adjectives like useless and doubtless are simply more marked than most, such that we permit comparative forms only in very limited contexts. However, I'm open to the possibility that some gradable antonyms really are anchored at one end by an absolute, uncomparable adjective. Does one of these theories have more merit than the other? Or are we just saying tomayto, tomahto?
Update: Thanks to ruakh for helping my organize my thoughts on this question. Essentially, I noticed that there are three kinds of adjectives that are similar in form and meaning but with different limitations in common usage. Some (doubtless) are listed in dictionaries as having no comparative form at all. Others (useless) have legitimate comparative forms, but they sound awkward without other modifiers (a hammer is more useless than a screwdriver). Still others (thoughtless) sound entirely natural in comparative form (Bob is more thoughtless than Alice).
Because all of these examples naturally fall on a spectrum and share the same suffix, I suspect that these differences are a matter of convention rather than semantics, but I'm not sure. Ideally, I'd like to see an analysis of the non-comparable and less-comparable words, specifically: How common are they, how strongly do people avoid the comparative forms in practice, and what role does convention versus semantics play in determining their limitations?
Best Answer
I think John Lawler and others make a good point in that "antonyms" are vague, and I suspect that, despite the descriptivist intent, the question arises from a semantic issue.
From Wiktionary, an antonym is "a word which has the opposite meaning of another, although not necessarily in all its senses." Thus fast is an antonym of slow, but fast is also an antonym of eat. However, most of us wouldn't think about comparing speed with consumption. Useful can be interpreted as "having non-zero utility," which means the opposite of useless. However, useful can also mean "having a positive degree of utility" which is not the opposite of useless. So they are fine antonyms, but not opposite in all meanings. A more appropriate opposite for the comparative version of useful would be harmful or detrimental.
For the more descriptive questions, specifically regarding the "-ful" and "-less" suffixes, I suspect that use of these words depend on how these suffixes are commonly interpreted. "Doubtless" and "useless," for example, imply devoid of doubt and devoid of use. "Thoughtless" and "tasteless," for example, imply lacking thought and lacking taste. The latter pair would be more common in comparative relative to non-comparative use since one can be naturally seen as more or less lacking. The former pair is less commonly seen since it is less logical and descriptively less common (though not unthinkable) to be seen as more or less devoid (of course, cf. emptiest). In general the commonality of use seems to me in line with whether or not it is logical -- so I don't see them as necessarily in conflict.
However, one exception comes to my mind (not saying that there aren't others). When raukh mentioned "impossible" (p = 0), my first thought of an antonym was "certain" (p = 1). As someone more accustomed to speaking with statisticians, for me, it sounds awkward when someone says something is more or less certain. However, I recognize that both descriptively and formally, certain is a comparative adjective. Indeed, it seems that the use of certain as a comparative is more common than the use of uncertain as a comparative, although that appears to be in relative decline.
Additionally -- this is perhaps silly of me to think it needs stating -- choice of which words to use also depend upon the emphasis of the sentence, even for paired words. Whether someting is "more impossible" or "less possible" may, for some, have different connotations. Curiously, those words seem to be converging in frequency of use.