Linguist Alexander Vovin suggests that the ancient kingdom of Tamna, which ruled the island until the twelfth century, may have spoken a Japonic language that left a substrate influence on Jeju.

Yang Changyong, a linguist, speculates that Mongol influence played a significant role in the formation of Jejueo as a distinct language independent[23] from standard Korean.

[26] Kim Sang-heon (1570—1652), who from 1601 to 1602 served as the island's pacification commissioner,[c] gives six words in the "provincial language" with clear cognates in modern Jeju and also writes:[27] 謫人 申長齡 乃譯官也 嘗曰 「比島語音 酷以中華 如驅牛馬之聲 尤不可分辯云云 盖風氣與華不隔而然耶 曾爲元朝所據置官於此故與華相雜而然耶」... 所謂俚語者 但高細不可曉 "The exiled man Shin Jangnyeong was originally a government interpreter.

[33] The 1970s Saemaeul Undong, an ambitious rural modernization program launched by Park Chung Hee, disrupted the traditional village community where Jeju had thrived.

"[42] In 2018, the Endangered Languages Archive at SOAS University of London collected audio and video recordings of native Jeju speakers having everyday conversations, singing traditional songs, and performing rituals.

[44] In addition, many Jeju Islander migrate to mainland Korea for a number of various reasons such as education, employment, and marriage contributing to decline of the Jejueo language.

Phonological differences, such as variations in pitch accent and vowel distinctions, may lead to misunderstandings or difficulties in comprehension between Jeju natives and speakers of Standard Korean.

In contrast to the mainstream linguistic rules observed in mainland Korean, Jejueo maintains earlier grammatical structures and syntactic patterns that may lead to misunderstandings or confusion during conversations.

[49] A 2018 study suggests that even the verbal paradigm, among the more resilient parts of the substratum, may be in danger; the average middle schooler was more competent in the verb system of English, a language "taught only a few hours a week in school and in private tutoring institutions", than of Jeju.

When the same survey was readministered in 2015, 36.8% were very proud of the language,[53] and Jeju Islanders had become the most likely among South Korean dialect groups to have "very positive" opinions of the regional variety.

[67] The project encouraged the promotion of Jeju Language in schools by tasking the Education Bureau with several initiatives, including a training program for teachers.

These experiences have contributed to a distinct sense of identity and solidarity among Jeju Islanders, often manifesting in cultural expressions, artistic forms, and community rituals that reflect resilience and resistance against oppression.

Similar to the modern Korean script, Jeju orthographies have morphophonemic tendencies, meaning that transcribing the underlying morphology generally takes precedence over the surface form.

Some of these are found in Standard Korean, such as the insertion of [n] before i- or j- at most word-internal morpheme boundaries; the palatalization of /t/ to [dʑ] before an affixal -i; and the tensing of obstruents following certain morpheme-final nasals.

ᄇᆞᆰ-/pɒlk/ᄇᆞᆰ-/pɒlk/"to be bright"ᄇᆞᆰ고[pɒk̚k͈o]ᄇᆞᆰ고[pɒk̚k͈o]ᄇᆞᆰ언[pɒlɡən]ᄇᆞᆰ언[pɒlɡən]삶/salm/삶/salm/"life"삶[sam]삶[sam]삶이[salmi]삶이[salmi]나ᇚ/namk~~나ᇬnaŋk~~낭naŋ/나ᇚ ~ 나ᇬ ~ 낭/namk ~ naŋk ~ naŋ/"tree"남[nam~~낭naŋ]남 ~ 낭[nam ~ naŋ]남기[namɡi~~낭기naŋɡi~~낭이naŋi]남기 ~ 낭기 ~ 낭이[namɡi ~ naŋɡi ~ naŋi]-어ᇝ/əms/CONT-어ᇝ/əms/CONT데껴ᇝ가[tek͈jəmɡa]데껴ᇝ가[tek͈jəmɡa]데꼄서[tek͈jəmsə]데꼄서[tek͈jəmsə]바ᇧ/pask/바ᇧ/pask/"outside"바ᇧ[pat̚]바ᇧ[pat̚]밧기[pat̚k͈i]밧기[pat̚k͈i]Jeju traditionally has a nine-vowel system: the eight vowels of Korean with the addition of ㆍ /ɒ/,[91] a Middle Korean phoneme lost in Seoul in the eighteenth century.

Verb stems with final vowel /u/ or /ɨ/ take the yang allomorph if their Middle Korean forms were /ɒ/, thus conserving their original harmonic class while violating their current one.

Its phonological hierarchy is characterized by accentual phrases similar to those of Standard Korean, with a basic Low-High-Low-High tonal pattern varying according to sentence type, but there are also important differences in the two languages' prosody.

[125] ORD: ordinal numeral INTR: interrogative MED: medial demonstrative SE: sentence ender CE: canonical ending REP : reportive NPST: nonpast Jeju is typologically similar to Korean, both being head-final agglutinative languages.

[131] 쉐swe"cattle"+  궤기gwegi"meat"→  쉐궤기swe-gwegi"beef"쉐 + 궤기 → 쉐궤기swe {} gwegi {} swe-gwegi"cattle" {} "meat" {} "beef"다리dari"leg"+  빙bing"illness"→  다릿빙dari-t-bing"leg illness"다리 + 빙 → 다릿빙dari {} bing {} dari-t-bing"leg" {} "illness" {} {"leg illness"}앚-aj-"to sit"+  일il"work"→  앚인일aj-in-il"work done while sitting"앚- + 일 → 앚인일aj- {} il {} aj-in-il{"to sit"} {} "work" {} {"work done while sitting"}ᄌᆞᆷjawm"sleep"→  ᄌᆞᆷ주시jawm-jusi"sleepyhead"ᄌᆞᆷ → ᄌᆞᆷ주시jawm {} jawm-jusi"sleep" {} "sleepyhead"먹-meog-"to eat"→  먹쉬meog-swi"glutton"먹- → 먹쉬meog- {} meog-swi{"to eat"} {} "glutton"ᄃᆞᆺ-daws-"to be warm"→  ᄃᆞᆺ임daws-im"warmth"ᄃᆞᆺ- → ᄃᆞᆺ임daws- {} daws-im{"to be warm"} {} "warmth"(Examples from Yang C., Yang S, and O'Grady 2019 and Ko J.

[160] 책광chaek-gwangbook-COM가방광을gabang-gwang-eulbag-COM-ACC주다ju-dagive-SE책광 가방광을 주다chaek-gwang gabang-gwang-eul ju-dabook-COM bag-COM-ACC give-SE"Give books and bags"지슬광jiseul-gwangᄃᆞᆨ세기dawksegi지슬광 ᄃᆞᆨ세기jiseul-gwang dawksegi"potatoes and eggs"낭ᄒᆞ고nang-hawgok고장gojangᄒᆞᄊᆞᆯhawsseul싱그라.singgeu-ra낭ᄒᆞ고 고장 ᄒᆞᄊᆞᆯ 싱그라.nang-hawgok gojang hawsseul singgeu-ra"Please plant some trees and flowers.

"The Jeju verb consists of a root that is followed by suffixes that provide grammatical information such as voice, tense, aspect, mood, evidentiality, relative social status, and the formality of the utterance.

[172][173][174] Depending on the analysis of the aforementioned epenthetical vowels that precede many verbal suffixes, the base forms of the three morphemes may alternately be analyzed as 엄시 -eomsi, 어시 -eosi, 크 -keu, and 느 -neu.

[187] Some analyses treat the initial vowel of the following suffix as part of an allomorph or nuanced variant of -(eu)k, so that 가커라 gakeora "[I] will go" may be segmented as ga-k-eora or ga-keo-ra.

The existence of the Korean subject-honorific marker (으)시 -(eu)si is controversial for Jeju, with some scholars arguing that it was entirely absent and others that it was restricted to higher registers.

[268] -masseum (variants 마씸 -massim, 마씨 -massi) may occur after subsentential phrases such as a bare or case-inflected noun, or attach to a small number of mostly plain sentence enders.

"[309] A major distinction between Jeju and Korean kinship terms is that women do not use honorifics to refer to their in-laws, reflecting weaker historical influence from Confucian patriarchal norms.

"느 송ᄉᆞ만이 전맹이 ᄀᆞᆺ 서른이 매기난, 서른 나는 해에 아무ᄃᆞᆯ 아무날은 맹이 매기니 느가 발 살앙 오몽ᄒᆞ여질 때, 나를 낭곳으로 ᄀᆞ져다 도라... 시 ᄆᆞ슬 강 심방 시 개 걷우우곡 마당이 큰대 세왕 두 일회 열나을 굿을 ᄒᆞ라..."맷딱 ᄎᆞᆯ려놓완 백보 밲겼딜로 간 절을 ᄒᆞ연, ᄀᆞ만이 꿀련 업더져두서 보난 삼체ᄉᆞ가 ᄂᆞ려오멍..."송ᄉᆞ만이네 집이서 정성을 아니드렴신가?

그 백년대강이가 송ᄉᆞ만이 심으레 오람센 ᄀᆞᆯ아분 생이여... 받음은 받았주마는 심엉 오랜 ᄒᆞᆫ 시간이 시여부난 어떵흘코?

""너 송사만이는 겨우 서른이 수명의 끝이니, 서른 되는 해에는 아무 달 아무 날에 명이 끝날 테이므로 너가 발이 살아서 움직일 수 있을 때 나를 나무숲으로 데려다 달라... 마을 세 곳에 가서 무당 세 명을 모으고 마당에 큰 깃대 세워서 두 이레 열나흘 굿[제주 큰굿]을 하라..."다 차려놓은 체 백보 바깥으로 가 절하며 가만히 무릎 꿇고 업드리고 보니까, 삼차사가 내려오면서..."송사만이네 집에서 정성을 드리고 있는 것 아닌가?

그 백년 된 해골이 송사만이 잡으러 오고 있다고 말해버린 모양이야... 준 건 받았지만 잡아 오라고 한 마감이 있는데 어떻게 할까?