The geographically proximate languages of Japanese (part of the Japonic languages) and Korean (part of the Koreanic languages) share considerable similarity in syntactic and morphological typology while having a small number of lexical resemblances. Observing the said similarities and probable history of Korean influence on Japanese culture, linguists have formulated different theories proposing a genetic relationship between them. These studies either lack conclusive evidence or were subsets of theories that have largely been discredited (like versions of the well-known Altaic hypothesis that mainly attempted to group the Turkic, Mongolian and Tungusic languages together)."While 'Altaic' is repeated in encyclopedias and handbooks most specialists in these languages no longer believe that the three traditional supposed Altaic groups, Turkic, Mongolian and Tungusic, are related." Lyle Campbell & Mauricio J. Mixco, A Glossary of Historical Linguistics (2007, University of Utah Press), pg. 7."When cognates proved not to be valid, Altaic was abandoned, and the received view now is that Turkic, Mongolian, and Tungusic are unrelated." Johanna Nichols, Linguistic Diversity in Space and Time (1992, Chicago), pg. 4."Careful examination indicates that the established families, Turkic, Mongolian, and Tungusic, form a linguistic area (called Altaic)...Sufficient criteria have not been given that would justify talking of a genetic relationship here." R.M.W. Dixon, The Rise and Fall of Languages (1997, Cambridge), pg. 32."...[T]his selection of features does not provide good evidence for common descent" and "we can observe convergence rather than divergence between Turkic and Mongolic languages--a pattern than is easily explainable by borrowing and diffusion rather than common descent", Asya Pereltsvaig, Languages of the World, An Introduction (2012, Cambridge) has a good discussion of the Altaic hypothesis (pp. 211-216). New research revived the possibility of a genealogical link, such as the Transeurasian hypothesis (a neo-Altaic proposal) by Robbeets et al., supported by computational linguistics and archaeological evidence, but it has many critics.Robbeets, Martine and Bouckaert, Remco. Bayesian phylolinguistics reveals the internal structure of the Transeurasian family , Robbeets, Martine et al. 2021 Triangulation supports agricultural spread of the Transeurasian languages, Nature 599, 616–621

However, there is also more traditional comparative research affirming a genetic link between Japonic and Koreanic, see .

Korean and Japanese have very different native scripts (Hangul and kana, respectively), although they both make use of Chinese characters to some extent; Kanji still are a core part of modern Japanese orthography, while Hanja were historically used to write Korean. Today, Hanja are only used in South Korea for limited academic, legal, media, stylistic and disambiguation purposes and are not used at all in North Korea. Although both Hangul and the two modern kana systems (katakana and hiragana) show syllable/mora boundaries, Hangul syllable blocks break down into a featural alphabet, while the kana are essentially pure syllabaries.

Overview

Korean Japanese Speakers 83 million 126.4 million Countries Family Koreanic Japonic Writing Hangul,Hanja (South Korea), Idu, Gugyeol, Hyangchal (formerly) Kana,Kanji, Man'yōgana (formerly)

Grammar Korean and Japanese both have an agglutinative morphology in which verbs may function as prefixesBernard Comrie: "Introduction", p. 7 and 9 in Comrie (1990). and a subject–object–verb (SOV) typology.S. Tomlin, Russell. Surveyed in the 1980s.Introducing English Linguistics International Student Edition by Charles F. MeyerRussell Tomlin, "Basic Word Order: Functional Principles", Croom Helm, London, 1986, page 22 They are both topic-prominent, null-subject languages. Both languages extensively turn nouns into verbs via the "to do" helper verbs (Japanese suru する; Korean hada 하다).

Vocabulary The two languages have been thought to not share any cognates (other than loanwords), for their vocabularies do not phonetically resemble each other.

However, a 2016 paper proposing a common lineage between Korean and Japanese traces around 500 core words thought to share a common origin. Most resembling lexicon in the study has been observed between Middle Korean (15th century) and earlier Old Japanese (8th century), some of which is shown in the following table: Keyword Middle Korean Old Japanese ProposedProto-Japanese-Korean abandons stú("scoops it out, removes a part from the whole") sute("abandons it, throws it away") *sɨtu("abandons it, throws it out") adds kwop("doubles, increases it two-fold") kupape("adds it") *kop("increases it in number by adding") (adjectivizer) k("adjectivizing suffix on nominals") ka("property suffix on nominals") *k("adjectivizing suffix on nominals")+ *a("deverbal") avoids skúy("shuns, avoids; is unwilling") sake("avoids, dodges") *səka("avoids") bamboo táy("bamboo")?< *taGVy takey("bamboo") *takəj basket kwulek("[mesh] basket") kwo("basket") *kura / *kuwa("basket") bear kwom("bear")< Proto-Korean *komá kuma("bear") *koma("bear") below aláy("below") aye("falls to the ground") *ar("below") bestows kwomá("reverence"),kwómáw("honored, thankful") kubar / kumar("apportions and bestows") *kuma("bestows") bird say("bird") sagi("heron; suffix in bird names") *saŋi("bird") bites kemelí("leech"),kam-spol("licks it up, sucks up food") kam("bites") *kamɨ("bites") body mwóm ("body") < Old Korean *muma mu- / mwi("body") *mom("body") boils it nóy("smoke, vapor") ni("boils it") *nəj("boils it") bottom stáh("ground") sita("below, bottom") *sita("bottom") box pakwoní("basket") pakwo("box") *pako("box") brings into life wum("a sprout, a shoot, a growth") um("gives birth to, brings into life") *um("brings into life") bundles mwusk("binds it into a bundle") musub("binds it into a bundle") *musu("binds, bundles it") buries it wumúl("well"),wúmh("grain pit dug out of the ground"),wumwuk-ho("is hollow") ume("buries it in the ground") *umu("buries it in the ground") cage wulí("cage") wori("cage") *orɨj("cage") carbon swusk("charcoal") susu("soot") *susu("soot; carbon") carries on back ep("bears, carries on the back") op("bears on the back") *əp("carries on back") carves a line kuzu("draws a line, rules") kizam("carves"),kisage("shaves stone") *kinsɨ("carves, cuts a line") cat kwoy("cat") nekwo("cat") *ko("cat") ceremony kwús("exorcism, shamanistic ceremony") kusi("is strange, mysterious, otherworldly") *kusuj("shamanistic ceremony") changes kaph("returns it, pays it back") kap("buys it"),kape("exchanges, changes it"),kapar("it changes") *kap("it changes, changes hands") cheek pwól("cheek") popo < *po-po("cheek") *por("cheek") chicken tolk("chicken") tori("bird, chicken") *tərəŋ("chicken") closes it tat("closes it") tat("interrupts, cuts off, finishes it") *tat("closes it") cloth swowom("cotton") swo("clothing; cloth; hemp") *so("cloth") cloudy skí("gets dusty, cloudy") sike("sky gets cloudy") *siki("gets cloudy") collects kat("collects it, gathers it in") kate("joins it, mixes it, adds it in") *kat("collects") comes ká("goes") ko("comes") *kə("comes") confines kalm("hides it, puts it away, keeps it, treasures it") karame("arrests it, catches and confines it") *karama("confines it") congeals kel("thickens, congeals; is rich, thick") kor("it thickens, congeals") *kərɨ("it thickens, congeals") correct mac("is correct"),maskaw("is correct") masa("correct, upright") *masa("correct, upright") countryside wúy ánh("countryside") wi naka("countryside") *uj("countryside") + inside daytime nác("daytime; afternoon")