Reduplication in Japanese

In Japanese, sometimes you have words that repeat themselves, they're the same thing said twice, like: hitobito 人々, iroiro 色々, betsubetsu 別々, marumaru 丸々, dandan 段々, hibi 日々, tsugitsugi 次々, itaitashii 痛々しい and so on.

When such thing happens, it's called reduplication, or choujou 重畳, the process of creating "reduplicative words," jougo 畳語, and it's not specific of the Japanese language. English has it too.

In this article I'll explain how it works in Japanese, and common effects it has on the meaning of words.

• Same Word Twice
• Repetition vs. Reduplication
• Same Kanji Twice
• Single Kanji Reduplication
• Single Kanji Not Simplex Form
• Repetition of Kana
• Change in Pronunciation
• Rendaku
• Sokuonbin
• Effect Patterns
• Plurals and Groups
• Groups of Individuals
  人々, 神々
• Geographic Groups
  国々, 島々
• Other Groups
  数々, 隅々
• Parallels and Alternatives
• Reduplicative Alternatives
  様々, 色々
• Reduplicative Parallels
  別々, それぞれ
• Emphasis
• Adverbs from Adjectives
  丸い to 丸々
  軽い to 軽々
• -shii ～しい Adjectives
  騒々しい, 痛々しい
• Other Emphatic Words
  少々, 満々
• Continuity
• Sequences, Frequencies, Progresses
  日々, 次々, 益々, 代々, 順々
• Indefinite Infinite Repetition
  ドキドキ, わくわく
• Definite Unreduplicated Finite
  ドキっと
• References
• Notes

Same Word Twice

The reduplication in words works like this: you have a word, like tsugi つぎ, "next," and when you say it twice: tsugi-tsugi つぎつぎ, it means "in succession," something rather different instead. It doesn't mean "next next" as we'd expect.

This happens because tsugi つぎ and tsugi-tsugi つぎつぎ are two different words that share the same morpheme. A morpheme is like a piece of a word. The word tsugi has the morpheme tsugi once, while the word tsugi-tsugi has the morpheme tsugi twice.

Linguistically, the two parts of tsugi-tsugi, the first tsugi and the second tsugi, are called base and reduplicant. When you remove the reduplicant of a reduplicative word, you get its simplex form.

• tsugi-tsugi, "in succession," a reduplicative word
  minus the reduplicant morpheme -tsugi
  equals tsugi, "next," the simplex form.

A couple more examples of reduplication in Japanese:

• naka-naka なかなか (reduplicative word.)
  Considerably.
• naka なか (simplex form)
  Inside.

• yama-yama やまやま (reduplicative word.)
  Mountains.
• yama やま (simplex form)
  Mountain.

Repetition vs. Reduplication

Note that there's a technical difference between words that feature reduplication and words that just feature repetition of syllables. But honestly that doesn't matter very much as far as this article is concerned since the word we'll be talking about share the same properties anyway.

See the References for the details.

Same Kanji Twice

In Japanese, words are often written with kanji, not without kanji like I wrote them above. When reduplication occurs, the kanji are duplicated too. Fortunately, in most cases one kanji represents one morpheme, so the all you gotta do is literally write it twice:

• tsugi 次
• tsugi-tsugi 次次

Since reduplication is found in a ton of Japanese words, and reduplicating the morpheme means you must write the kanji you just wrote all over again, BY HAND, the Japanese people figured "yeah, nah, ain't nobody got time fo' dat," and decided to use a symbol instead when reduplication occurred in a word.

This symbol: 々, called kurikaeshi 繰り返し, "repetition," or noma ノマ, because of how it looks, is used instead of the kanji that represents the reduplicant in a word. For example:

• tsugi-tsugi 次々
  is the same as tsugi-tsugi 次次.
• naka-naka 中々
  is the same as naka-naka 中中.

This can also happen in the middle of the word:

• issakujitsu 一昨日
  The day before yesterday.
  Two days ago.
• issakusakujitsu 一昨々日
  The day before before yesterday.
  Three days ago.

Sometimes the base is composed of more than one kanji (and/or morpheme), so the reduplicant is longer too. Although it's not considered valid anymore since the post-war orthographic reforms, the number of kurikaeshi's for the reduplicant could then match the number of kanji in the base.

• hitori 一人
  One person.
• hitorihitori 一人一人
  hitorihitori 一人々々
  For each person. To each person.

• baka 馬鹿
  Idiot. (person.)
• bakabakashii 馬鹿馬鹿しい
  bakabakashii 馬鹿々々しい
  Foolish. (Thing to say/think.)

Note that although reduplication is common in Japanese words, triplication, the same thing thrice, is not.

Single Kanji Reduplication

Sometimes a single kanji represents a single morpheme, sometimes more than a single morpheme, and, in some very weird cases, a single kanji represents the same morpheme twice.

• somosomo 抑
  To begin with, (nobody said this couldn't happen.)
• iyoiyo 愈
  At last. Finally.

The examples above are usually not written with kanji, though, specially not one kanji. They're normally written with kana. So although it's possible for them to be written like that, that doesn't mean they will be written like that.

Single Kanji Not Simplex Form

If a reduplicated word is written by writing a same kanji twice, then it'd make sense to think that writing that kanji only once is how you'd write the simplex form.

But that's not always the case.

For example:

• sugasugashii 清々しい
  Refreshing.

Although sugasugashii is a word, suga is not. How can that be? Furthermore, the readings of the kanji of that word, 清, don't even include suga! That is: there's no other word in Japanese where 清 is read as suga. What is the world is going on here?!

Well, apparently, the suga すが of sugasugashii comes from the sugi of sugisaru 過ぎ去る, "to pass by," or "to pass and leave." ^{(清々しい - yuraika.com)}

By reduplicating this suga into suga-suga the meaning became emphasized. And the -shii ending makes it refer to what something feels like. So maybe sugasugashii means it feels "refreshing" because whatever problem was there has passed and gone away.

Anyway, this suga isn't used in Japanese anymore, but sugasugashii stuck. That's why the word sugasugashii still exists but suga does not.

Since the word sugasugashii exists, it feels bad for it not to have kanji. So someone slapped a "matching character" on it, an ateji 当て字, which was 清, for its "clear" meaning matched the "refreshing" meaning of the word.

So that's why the simplex form isn't written as suga 清. The 清 is only read as suga in the word sugasugashii 清々しい, not when it's written alone, so that's a "compound character reading," jukujikun 熟字訓, a reading that's only valid in a specific combination of characters. (清々しい in this case.)

Repetition of Kana

There are other iteration marks in Japanese besides 々, some of which can be used to express reduplication in words written without kanji, with just kana. But those aren't really common so I won't talk about them. Mentioning them is enough I guess.

Change in Pronunciation

Reduplication doesn't always reduplicate the simplex form exactly (full reduplication). Sometimes a change in pronunciation occurs (partial reduplication).

For example, the English words tick-tock, ding-dong, and zig-zag feature ablaut reduplication, in which the vowel changes. ^{(The language rules we know – but don't know we know - bbc.com.)}

In Japanese, the vowels do not change in words featuring partial reduplication. Instead, it's the consonants that change. This can happen in two ways:

1. A consonant gets diacriticized.
2. A consonant gets geminated.

Rendaku 連濁

The first and most common case is called rendaku 連濁, a change in pronunciation where the first syllable of a suffixed morpheme can get a diacritic, a dakuten ゛ mark (or handakuten ゜).

For example:

• kami 神
  God.
• kami-kami 神々
  (wrong.)
• kamigami 神々
  Gods.
  (ka か became ga が)

• toki 時
  Time.
• toki-toki 時々
  (wrong.)
• tokidoki 時々
  Sometimes.
  (to と became do ど)

• tsukudzuku 熟
  Utterly.
  (tsu つ became dzu づ)

This rendaku effect is by no means a reduplication-only thing. It happens in words without reduplication too. For example, the word for "God of Death" is shinigami 死神, not shini-kami.

Which morphemes get rendaku'd varies. In particular, mimetic words, which frequently repeat themselves, do not feature rendaku in their repeated parts. Example: karikari かりかり, *scratching,* doesn't become karigari.

Furthermore, it's a word that features rendaku, not the combination of morphemes or the repetition of a certain kanji. That is, although rare, you can have two different words spelled the same way, homographs, both featuring reduplication, but one pronounced with rendaku (partial reduplication) and the other without (full duplication).

For example:

• sama-zama 様様 / 様々
  Various.
  (this word features rendaku)
• sama-sama 様様 / 様々
  Thankful. Gracious. Good to have. (suffix added to things to mean they're welcomed. E.g.: money, clear weather, etc.)
  (this word doesn't feature rendaku.)

This would be really confusing, wouldn't it? To make things clearer, although the spellings 様々 and 様様 should be interchangeable for both words, it's common to spell the latter without kurikaeshi. I.e.: samazama 様々 and samasama 様様.

Sokuonbin 促音便

The second case is called sokuonbin 促音便, a change in pronunciation where two sequential hard syllables of different morphemes in the same word get melded together (consonant gemination) into a double consonant instead.

Such "double consonants" are represented in Japanese by a small tsu っ, and in romaji by literally spelling the consonant twice.

As far as I know this only happens in one reduplicative word:

• koku 刻
  Approximately two hours. (archaic meaning.)
  (the kanji means "moment," though, like...)
• ikkoku 一刻
  One moment.
  (ichikoku いちこく became ikkoku いっこく)
• ikkoku mo hayaku 一刻も早く
  As soon as possible.
  Even one moment faster. (literally.)
• kokkoku 刻々
  Moment by moment.
  (kokukoku こくこく became kokkoku こっこく)

(And that's the name of a certain amazing anime: Kokkoku 刻刻)

Effect Patterns

Now, moving to the main part of the article: the common effects of reduplication.

Japanese words that repeat themselves always exhibit one sort of another of multiplicity in their meanings. After all, if you say one thing once, you imply one of it, but when you say it twice, you imply you have two (or more) of it.

In practice, this makes most reduplicative words into:

1. Plurals, collectives of their simplex forms.
2. Parallels or alternatives based on the simplex forms.
3. Emphasized versions of the simplex forms.
4. Sequences or continuity according to the frequency of the simplex forms.

Plurals & Groups

Let's start with Japanese reduplicative plurals. But this needs a bit of a warning.

The way how plurals work in Japanese is that most words do not have plural forms. Combined with the lack of definite and indefinite articles, a single random noun, like neko 猫, "cat," can refer to one cat, a random cat, the cat, the cats, some cats, or even all cats, like, in general, etc. depending on the sentence.

• neko ga iru 猫がいる
  There's a cat [here.]
  There are cats [here.]
  The cat is [here.]
  The cats are [here.]
• neko ga suki 猫が好き
  I like cat. (this doesn't make much sense.)
  I like cats.

So, for most words, you don't really need do anything to get the plural version because plurality depends on context. Furthermore, you can't just reduplicate a random word to make it plural. You can't say neko-neko 猫々, for example, to mean "cats." That word doesn't exist.

Anyway, back to words that do exist. Some words that feature reduplication are plural versions of their simplex forms. This does happen. Yes. But they aren't just "plurals," they're more like "groups," they describe collectives, many of something, usually implying various of something, too.

Individuals

For example, it happens when referring to individuals and their collectives, like:

• kami 神 vs. kami-gami 神々
  A god vs. many, various gods.
  (each god is different from the other.)
• hito 人 vs. hibo-bito 人々
  A person vs. many, various people.
  (each person is different from the other.)
• ware 我 vs. ware-ware 我々
  I vs. we. (this is one of the many first person pronouns found in Japanese.)
• kata 方 vs. kata-gata 方々
  Person (related to something, somewhere.) vs. people.
  (these words are like ware and ware-ware but used toward others instead.)

Above we have words that refer to "groups" of stuff. For example, when one says kamigami, they aren't referring to two random gods in particular, they're probably referring to all the gods of the Olympus, or all Japanese gods,"or "going against the gods" in general—heresy!—"the battle of the gods," etc.

• Ragnarök
  Fate of the Gods
  Kamigami no Unmei 神々の運命

Likewise, hitobito aren't two persons, they are the many people (of somewhere, for example, like a village). And wareware doesn't refer to two of "me," it probably refers to the group I represent: my company, organization, institution, etc.

Geography

This form is also common with geographic words.

• kuni 国 vs. kuni-guni 国々
  A country vs. many, various countries.
• shima 島 vs. shima-jima 島々
  An island vs. many, various islands.
• yama 山 vs. yama-yama 山々
  A mountain vs. many, various mountains.
• ki 木 vs. ki-gi 木々
  A tree vs. many, various trees.
• hoshi 星 vs. hoshi-boshi 星々
  Star vs. many, various stars.

Such words are generally qualified by adjectives. For example:

• yooroppa no kuni-guni ヨーロッパの国々
  The countries of Europe.
  The many, various countries of Europe.
  (each one is different from the other.)

Likewise:

• yooroppa no hito-bito ヨーロッパの人々
  The people of Europe.

Other

Some more examples of reduplicative words expressing plurality:

• kazu 数
  A number.
• kazu-kazu 数々
  Many numbers of.
  Numerous.
• kazukazu no tatakai wo kachi-nuite-kita 数々の戦いを勝ち抜いてきた
  To have come [here after] winning through many numbers of battles
  To have won and survived numerous battles.

• sumi 隅
  Nook. Corner.
• sumi-zumi 隅々
  The nooks of. The corners of.
• heya no sumi-zumi made sagase!! 部屋の隅々まで探せ！！
  Search EVERY SINGLE LAST CORNER of this room!!
  Search even the corners of the room!! (literally.)

• kona 粉
  Flour. Dust.
• kona-gona 粉々
  Small pieces.
• kona-gona ni shite yaru!!! 粉々にしてやる！！！
  [I'll tear] you into pieces!!!

Parallels & Alternatives

In Japanese, there are some words which feature a rather weird effect when they are reduplicated. They become plurals, sure, sort of, but the way they end up being used are as adjectives or adverbs rather than nouns.

This happens in words such as iroiro 色々 and betsubetsu 別々. And it happens because the simplex forms means one "type" of thing, rather than one "thing" of one type. When you reduplicate, the collective is then the various "types" of things, rather than various things of one type.

In practice, the outcome is that such words end up having either of the following effects:

1. Alternatives.
   I.e. multiple types simultaneously.
2. Parallels.
   I.e. multiple ways simultaneously.

Alternatives

The first case, for alternatives, is a bit complicated because the simplex forms are complicated to begin with.

Let's start with an example:

• samazama na dougu 様々な道具
  Various types of tools.
  Various kinds of tools.

Above we have the reduplicative samazama as adjective for the tools. It means "various types" or "various kinds."

The simplex form of samazama is the word sama 様. But wait... sama? The honorific suffix like san, chan, or kun? What? How do you get "various types" from that?! It doesn't even have an actual meaning, just a nuance!

Well, no. The suffix sama is a different sama, not the one we're talking about here. The word sama 様 also means how something looks like, appears like. It's found in words like arisama 有様, "the way something is," literally "appearance of being."

So let's say you have a bunch of tools. This tool looks one way, that's looks this sama. This tool looks another way, it looks this other sama. So here we have tools that look this sama and that sama, that's two sama way-of-looking, samazama.

That's the gist of it.

Next we have this:

• iroiro 色々
  All sorts of.

Alright, so the simplex form of that is more simple, I mean, it's iro 色, "color."

So why does it not mean "colors"? What's up with this "all sorts of"? That makes no sense! The word iro means "color," not "sort," what is this madness!!!

Well, actually, the word iro also means "sort." (and, also-also, iroiro used to mean "colors," but that usage is archaic, so let's ignore it.)

You can find it in the following yojijukugo 四字熟語, "four-character idiom:"

• juu-nin to-iro 十人十色
  Ten people, ten colors.
  (i.e. each person has their own tastes, interests, ideas, opinions, etc. each has their own "color.")

So, likewise, iroiro 色々 is the collective of "sorts."

• iroiro atta 色々あった
  All sorts of [things happened.]
  There were all sorts. (literally.)

Parallels

Next we have these words:

• betsubetsu 別々
  Separately.
• sorezore 夫々
  Each.
• koko 個々
  One by one.
• tokorodokoro 所々
  Here and there. Everywhere.

The word sore それ means "that." Imagine there's a bunch of things in a room. You point to one, you say sore, "that." Then the next one, sore, "that." The next: sore. And sore. And sore. And that, that, that. In other words, you're referring to "each" of them individually, in parallel, rather than collectively.

• sorezore no yakuwari ga aru それぞれの役割がある
  Each has a role. (literally.)
  Everybody has their own role.
  Everything has its own role.

The word betsu 別 means "different," or "separate" of something else. So betsubetsu 別々 implies we have two (or more) betsu's.

For example, if this guy is acting betsu, "separate," of this other guy, who's acting betsu, "separate," of this third guy, and so on. They're acting betsubetsu of each other, separately.

• toire ga betsu no heya ni aru トイレが別の部屋にある
  The toilet is in a different room.
• basu ga betsu no heya ni aru バスが別の部屋にある
  The bath is in a different room.
• ofuro to toire ga betsubetsu お風呂とトイレが別々
  The bath and and the toilet are separate.

With tokorodokoro 所々 we're implying there's a tokoro 所, "spot," "place," here, a tokoro there, a tokoro over there, and they all have something in common. For example, if you slip on a banana peel and drop a bucket of paint, now there's paint "everywhere," there's paint tokorodokoro. The paint is in multiple places at once.

Emphasis

The next common effect reduplication has is of making things intense. Intenser. Importanter. Very-er. As the saying says, when you say something twice it's because it's important.

It's because it's important!

Adverbs from -i Adjectives

In practice, this means that when the base morpheme of a reduplication is also the stem of an -i ～い adjective, the reduplicative word may add emphasize to that adjective. For example:

• maru 丸 (simplex form.)
  Circle.
• marui 丸い (base morpheme + -i suffix)
  Round.
• marumaru 丸々 (reduplicative word)
  Round-round (like a record, baby, no! Like a ball. 3D.)
  Rotund. Very round.

Note that this base morpheme (simplex form) won't necessarily be a word on its own. (and usually isn't.) That is, the base morpheme plus the -i suffix is a word, but without the -i suffix it may not be a word. For example:

• naga 長 (simplex.)
  (this isn't a word, just a morpheme.)
• nagai 長い (i-adjective)
  Long.
• naganaga 長々
  Very long.

• hiro 広
  (not word.)
• hiroi 広い
  Spacious.
• hirobiro 広々
  Very spacious.

• atsui 熱い
  Hot.
• atsuatsu 熱々
  Very hot.
  (e.g. food that you just cooked.)
  (also used toward couples burning with passion.)

• hosoi 細い
  Thin.
• hosoboso 細々
  Very thin.

• karui 軽い
  Light.
• karugaru 軽々
  Very light.
  (e.g. to lift something) as if it were light.
  (by extension, to do something difficult) as if it were easy.
  Lightly. Easily.

Since all cases above express how something is perceived, they may all take the to と particle to become adverbs in which modify how an action is perceived. For example:

• marumaru to futotta 丸々と太った
  [He] fattened [to the point he looked] very rotund.
• karugaru to mochiageta 軽々と持ち上げた
  [He] lifted [it] up [as if it were] very light.

-shii ～しい Adjectives

The to と particle above was used to adverbalize reduplicative words that are perceivable. In contrast, the suffix -shii ～しい adjectivizes them.

Look: -shii ～しい ends in -i ～い, so it makes -i adjectives.

What comes out of reduplicating something and adding -shii ～しい on top of it can vary wildly. Of course, they are somewhat, somehow related to their simplex forms, but their usage can be pretty different.

Here are some examples to have a better idea:

• itai 痛い
  Painful. Hurting.
  Cringy,
• itaitashii 痛々しい
  Painful to look at. (e.g. injuries.)
  Pitiful.

• maga 禍
  Disaster. Calamity.
• magamagashii 禍々しい
  Ominous. Sinister.

The perception isn't limited to what it looks like. It could also be what you hear:

• sawagu 騒ぐ
  To make noise.
• sou-on 騒音
  Noise (sound.)
• souzoushii!! 騒々しい！！
  Too noisy!!
• shizuka ni se yo!! 静かにせよ！！
  Be silent!!
  (— Overlord, Season 3)

Or what you feel, think, etc.

• hanayaka 華やか
  Showy. Gorgeous.
• hanabanashii 華々しい
  Magnificent.
  To feel very showy.

• oogyou 大仰
  Exaggeration.
• gyougyoushii 仰々しい
  Extravagant.
  To feel very exaggerated.
  

• baka 馬鹿
  Idiot.
• bakabakashii 馬鹿馬鹿しい
  Foolishness.
  To feel very stupid.

A good number of words that follow this pattern can be used to make comments toward other people—a lot of times bad, uncalled for comments—according to what their appearance or behavior looks like. For example:

• utsukushii 美しい
  Beautiful.
• bi 美
  Beauty.
• bibishii 美々しい
  Of seeming beauty.

• wakai 若い
  Young.
• wakawakashii 若々しい
  Of seeming youth.

• yowai 弱い
  Weak.
• yowayowashii 弱々しい
  Of seeming frailty.

• me 雌 / 女
  Female. (affix.)
• onna 女
  Woman.
• mesu 雌
  Female. (animal.)
• megami 女神
  Goddess.
• memeshii 女々しい
  Of seeming femininity.
  Effeminate.

• o 雄 / 男
  Male. (affix.)
• otoko 男
  Man.
• osu 雄
  Male. (animal.)
• dokuo 毒男
  Single male. dokushin dansei 独身男性.
  (self-derogatory internet slang.)
• ooshii 雄々しい / 男々しい
  Of seeming manliness.
  Manly.

• rinzen 凛然
  Commanding. Awe-inspiring.
• ririshii 凛々しい
  Someone that looks heroic, dignified.
  (e.g a protagonist of a Hollywood action movie, Superhero comic book, the good guy. Hercules, Superman, Wonder Woman, etc.).

• kai 甲斐
  Effect. Result. Worth.
• kaigaishii 甲斐甲斐しい
  That seems to prove its worth.
  Hard-working. Admirable. Laudable. Dependable.

• nareru 馴れる
  To become familiar with.
• narenareshii 馴れ馴れしい
  To seem over-familiar. (generally in a bad way.)
• Example: talking in a way that's too informal, invading your personal space—PERSONAL SPACE!!!—touching, etc.

• karui 軽い
  Light.
• karugarushii 軽々しい
  Rash. Thoughtless.
  (i.e. takes everything lightly, doesn't give proper consideration.)

Other Emphatic Words

There are other reduplicative words that intensify things in a way or another but don't fit the cases above. For example:

• mukashi 昔
  A long time ago.
• mukashi-mukashi 昔々
  Long, long ago (in a galaxy far, far away...)
  (generally used to tell tales, i.e. "once upon a time.")

• mae 前
  Before.
• mae-mae 前々
  Since much before.

• man- 満～ (prefix.)
  Whole.
• manman 満々
  Full of. Brimming with.
• yaru ki manman da ne やる気満々だね
  [You're] full of will to do [it, aren't you.]
  (i.e. eager.)

• hisashii 久しい
  For a long time.
  Since a long time.
• hisabisa 久々
  Since a very long time.

• sukoshi 少し
  A little.
  A bit.
• shoushou 少々
  A lil' bit.

• tadashii 正しい
  Correct. Right.
• seisei 正々
  Fair.
• dou 堂
  Shrine.
  Hall.
• doudou 堂々
  Honest. Proud. Unashamed.
• seisei-doudou tatakau 正々堂々戦う
  To fight fair and proudly.
  To fight fair and square.

Reduplicative Continuity

The last effect of reduplication in words is that of continuity. That is, the implication that something is going on, and on, and on, and on, and on, and on, and on, and on, and on, and on, and on, and on, and on, and on, and on, and on, and on, and on, and on, and on, and on, and on, and on, and on, and on, and on, and on, and on, and on, and on, and on, and on, and on, and on, and on, and on, and on.

You get it.

Surely, nothing goes on infinitely, forever, but stuff can go on indefinitely, for kamisama knows how long. In Japanese, reduplication of certain words can imply something happened continually for a unspecified amount of time, or refer specifically to the frequency by which it happened rather than for how long exactly.

Sequences, Frequencies, Progresses

Simplex forms that can imply time, degree, or mark a step of progress, and so on, can become adverbs of progression when reduplicated. For example:

• hi 日
  Day.
• hibi 日々
  Daily. Every day.

Note that there's a different word which also means "daily" or "every day," mainichi 毎日. The difference is that hibi 日々 implies progression, as the reduplication implies. That is, you have an indefinite, continuous, and sequential number of days:

hi 日, hi 日, hi 日, hi 日, hi 日, hi 日, hi 日, hi 日, hi 日, hi 日, hi 日, hi 日, hi 日, hi 日.

And hibi 日々 implies it.

So you could, for example, you can study "every single day," mainichi, but you make progress "daily, continuously," hibi. Likewise, there are scientific experiments being done "every single day," mainichi, but scientific advances are done "daily, continously," hibi.

Other examples of sequences implied by reduplication include:

• tsugi 次
  Next.
• tsugi 次 tsugi 次 tsugi 次 tsugi 次 tsugi 次
  Next. Next. Next. Next. Next.
• tsugitsugi 次々
  In succession. The next one, then the next, over and over.

• dan 段
  Grade.
• dan 段 dan 段 dan 段 dan 段 dan 段
  Grade. Grade. Grade. Grade. Grade.
• dandan 段々
  Grade by grade. Gradually.

• toki 時
  Time.
• toki 時 toki 時 toki 時 toki 時 toki 時
  Time. Time. Time. Time. Time.
• tokidoki 時々
  Time and again. Sometimes.

• tabi 度
  Occasion.
• tabi 度 tabi 度 tabi 度 tabi 度 tabi 度
  Occasion. Occasion. Occasion. Occasion. Occasion.
• tabitabi 度々
  Occasionally. Time and again.

• dai 代
  Generation.
• dai 代 dai 代 dai 代 dai 代 dai 代
  Generation. Generation. Generation. Generation. Generation.
• daidai 代々
  For generations.

• kaesu 返す
  To return.
• kaesu 返す kaesu 返す kaesu 返す kaesu 返す kaesu 返す
  To return. To return. To return. To return. To return.
• kaesugaesu 返す返す
  To do something over and over. (i.e. returning to the start, restarting, every time.)

• masu 益
  Increase.
• masu 益 masu 益 masu 益 masu 益 masu 益
  Increase. Increase. Increase. Increase. Increase.
• masumasu 益々
  Increasingly.

• jun 順
  Order. Turn.
• jun 順 jun 順 jun 順 jun 順 jun 順
  Turn. Turn. Turn. Turn. Turn. Turn.
• junjun 順々
  In turns. In order (of turns.)

Indefinite Infinite Repetition

Lastly, the same way as above, reduplication in mimetic words such as onomatopoeia naturally implies a continued idea or sound.

For example, wakuwaku わくわく, a mimetic reduplicative word for "excitement," implies that one waku = one excitement, and thus wakuwakuwakuwakuwakuwakuwakuwakuwaku means a continuous state of excitement.

More tangibly, dokidoki ドキドキ is an onomatopoeia for the *thump-thump* of the heart. But surely the heart doesn't just thump just twice and stops there. It keeps thumping. So dokidokidokidokidokidokidokidoki, etc.

Definite Unreduplicated Finite

Conversely, when an ideophone that's usually reduplicative appears only in its simplex form, it would emphasize it's just a single instance.

For example, a single doki would mean "a single thump," rather than continuous thumping. By extension, dokitto ドキっと, "with a (single) thump," is used when you experience a strong emotion, something exciting, like love at first sight, or scary, maybe, by emphasizing that lone, stronger thump.

In English, the equivalent is ironically "to have your heart skip a beat," rather than to have a beat like in Japanese. That is, both expressions refer to the same thing: it's such an outstanding single thump the next one gets delayed, messing the rhythm, as if it were skipped, but they sound like they're opposites.

References

• Form and Function of Reduplicated Nouns in Japanese
  A study where native Japanese speakers were asked to describe what many reduplicative words mean, and what they think made up reduplicative words (such as neko-neko) would mean if they were real words.

Notes

Since the focus of this article was show the common effects of reduplication in Japanese, I didn't bother to make sure whether a word is really reduplicative from a technical standpoint or merely features repetition of syllables. So long as the effects were similar for me it's enough.

In particular, I'm not sure whether words like the below are actually reduplicative:
waka-waka-shii 若々しい
The simplex waka 若 is not a word on its own.
Only the adjective wakai 若い is.

man-man 満々
Likewise this is just a prefix prefixed onto itself.

mukashi-mukashi 昔々
This isn't a word you'd use normally. It's only used in stories.
It could very much be like saying "a long, long time ago."
The "long" is repeated; "long-long" isn't a word.

But then again, it's not like Japanese lacks punctuation.
You could write mukashi, mukashi 昔、昔. Okay, maybe not.
You could write mukashi mukashi 昔　昔, with a space.
So maybe it is a reduplicative word, after all.

dokidoki ドキドキ, wakuwaku わくわく, etc.
Practically all mimetic words that repeat themselves don't really have simplex forms.

I mean, if wakuwaku has a reduplicant, -waku, then you should be able to remove it to get waku, the simplex, just like you can do with any other reduplicative word.

But waku doesn't mean anything at all alone. Nobody says just one waku to mean anything related to "excitement." It only makes sense when it's wakuwaku, or more waku.

I'm no linguist, but if my interpretation is correct, the simplex form of a reduplicative word need not to be an actual word, just a morpheme.

If that's the case, then it's probably valid too. Since a morpheme is something you can't divide further, and you can totally divide wakuwaku into two waku. Just like you can divide dokidoki into two doki.

If that's not the case then what I'm saying is all wrong and a number of these aren't reduplicative words. Not that it matters though, because in the end the observed effects of repeating parts of words are the same.

Even if wakuwaku isn't a reduplicative word, it still gives the impression of continuity and frequency, just like hibi 日々, a word that's certainly reduplicative.