Words can be like people. Some will always look on the bright side, while others take a more pessimistic view of things. Words that fall into this latter category possess what linguists call “negative polarity.” Don’t worry, this is not a severe psychological disorder but an entirely harmless grammatical condition, with no reported side-effects whatsoever, that means some words and expressions prefer to show up in negated sentences.
A textbook example is the adverb あまり(amari). If you don’t feel hungry and would like to qualify this a little bit, you could say あまりお腹が空いていない (Amari onaka ga suite inai, “I’m not very hungry”). However, even if you should, in fact, happen to be quite hungry, you cannot turn this into a positive statement as it stands. Though あまり is not impossible in non-negated environments, there are adverbs much more suited to strengthening an affirmative sentence. Try, for instance, 大変 (taihen), とても (totemo) or, more casually, めっちゃお腹空いてる (Mecha onaka suiteru. I’m very/totally hungry).
A similar case of negative polarity afflicts 必ずしも (kanarazushimo, necessarily). Let’s say you don’t agree with what someone said but want to make sure your disagreement won’t come across as too direct. Then you could say 私は必ずしもそう思わない (Watashi wa kanarazushimo sō omowanai, “I don’t necessarily think so”). Be careful not to confuse 必ずしも with the slightly shorter 必ず, which has no medical record of negative polarity, and in contrast, predominantly occurs in positive sentences.
A patient whose negative polarity has recently come to be seriously questioned is the term 全然 (zenzen). As purists claim, it is all but illegal to use this adverb without negation. Accordingly, 全然問題ない (zenzen mondai nai, no problem at all) is, well, no problem at all, whereas the positive semantic equivalent 全然大丈夫 (zenzen daijōbu, totally OK) is branded as unacceptable.
In this respect, it’s tempting to think that zenzen behaves very much like “at all” in English, where a statement like “It’s OK at all” is not particularly reassuring, neither psychologically nor grammatically. And yet the comparison is not quite feasible, as witnessed by the fact that the use of zenzen is very common in present-day spoken Japanese (see, for instance, https://www.japantimes.co.jp/
What’s more, recent research has even revealed that the term in the past used to occur more frequently in positive rather than negative constructions. That only started to change during the postwar years, when people first seemed to find fault with zenzen in affirmative sentences. So the whole idea that zenzen only works with negation should best be regarded as semantic hypochondria rather than a true case of negative polarity.
But let’s return to the clear cases. Here are a few more examples guaranteed to work exclusively with negation: 一切 (issai), 決して (kesshite), ちっとも (chitto mo), 少しも (sukoshi mo) and さっぱり (sappari). All of these can be used almost interchangeably to amplify a negative assessment a la “not in the least” or “not a bit.”
Also useful is めったに (metta ni), which means “rarely,” provided it can find a negation to team up with. Thus, あそこにはめったに行かない (Asoko ni wa metta ni ikanai) means “I hardly ever go there,” whereas めったに行く (metta ni iku) just means you still have to work on your grammar. The same applies when you try to use しか (only) without negation close at hand. Any attempt to turn the fact that you have 100円しかない (hyaku en shika nai, only ¥100 left) into a more affirmative message is bound to fail.
A fairly reliable pattern with respect to polarity is (に)も (negative) vs. でも (positive) in question words. The polarity is so strong here that it works even without an explicit “no” or “not” element. For instance, when you’re asked if you saw someone last night and you don’t want to admit you did, you could just say 誰も (dare mo). This will automatically be taken to mean “no one” (or more precisely, “anyone,” but with an in-built “not”) and thus will get you off the hook for now.
Also compare どこにもない (doko ni mo nai, nowhere) and どこにでもある (doko ni demo aru, all over the place), or どうにもならない (dō ni mo naranai, “This is not going anywhere”) and どうでもいい ( “I couldn’t care less”). And be aware that 何もない (nani mo nai, nothing) is not quite the same as 何でもない (nandemo nai, nothing in particular). I’ve seen more than one argument arise from the subtle difference between these two types of nothing.
Finally, negative polarity items also inhabit a couple of collocations. Best-known, perhaps, is 仕方がない (shikata ga nai, can’t be helped), which, sadly enough, rules out any chance that things ever could be helped. A comparable case is the apology formula 申し訳ない (mōshiwake nai, “I’m sorry”). Even if you may think something you did is excusable, you shouldn’t call it 申し訳ある (mōshiwake aru). If you do anyway, people will find that to be simply とんでもない (tondemonai, outrageous). Needless to say, no positive equivalent for this last one is available either.