日本語が難しいと思われる理由 日琉語族と五十音図Understanding Japanese Language Difficulty from a Historical Perspective

One major reason Japanese is considered challenging is its fundamentally different linguistic lineage. Unlike European languages such as English or French, which belong to the Indo-European language family, Japanese belongs to an entirely distinct language family known as the Japonic languages (“日琉語族,” Nichiryu-gozoku). The Japonic family encompasses not only Japanese but also the Ryukyuan languages (“琉球諸語,” Ryukyu-shogo), currently spoken in regions such as Okinawa and the Amami Islands, and it is believed these languages branched off at some point from a common ancestral language known as Proto-Japonic (“日琉祖語,” Nichiryu-sogo).

From the viewpoint of comparative linguistics, no systematic correspondences have been identified between Japanese and European languages in terms of vocabulary or phonological systems. Historical evidence has also increasingly clarified that Japanese developed independently from the Indo-European languages. Thus, Japanese is broadly classified under the Altaic languages and, more recently, grouped within the proposed macro-family known as Transeurasian (“ツラン語族,” Tsurango-zoku), though ongoing research continues to investigate these hypotheses. In other words, Japanese belongs to a distinct linguistic lineage separate from the Indo-European family, which contributes significantly to the difficulty that speakers of English or French face when learning Japanese. Simply put, its linguistic structure fundamentally differs from languages like English.

Then, did modern Japanese originate independently within Japan? Current research strongly supports the theory that Proto-Japonic, the ancestor of modern Japanese, arrived via the Asian continent during Japan’s ancient Yayoi period. It is generally assumed that Proto-Japonic was transmitted through the Korean Peninsula to Japan, especially northern Kyushu, around the 9th century BCE. This linguistic transmission aligns with archaeological evidence marking a historical transition from the Jomon period, lasting over ten thousand years, to the Yayoi period, characterized by an influx of communities from the continent. The emergence of Japanese thus strongly indicates the arrival of new people in the archipelago from the continent.

The roots of the Proto-Japonic-speaking people trace back to Northeast China, where they branched off from other ancestral languages (within the Transeurasian/Altaic group) and moved southward into the southern Korean Peninsula before migrating to Japan. Later, around the 5th century BCE, the Korean Peninsula experienced the arrival of Proto-Koreanic (“原始朝鮮語,” Genshi Chosen-go), a completely separate linguistic lineage from the continent, likely displacing and eventually eradicating Proto-Japonic as the indigenous language there. Thus, the origins of Japanese trace back to the Yayoi period, representing an entirely separate linguistic evolution from the Indo-European language spread observed across Europe.

But, this linguistic development is thought to have involved further intermixing with peoples from other, even more complex language lineages. Although the overall picture is gradually becoming clearer, understanding all the intricate details will require much more time. Some theories even suggest that the Jomon people themselves may have consisted of multiple groups. Thus, it could be said that the distinctive Proto-Japonic language emerged through the complex mingling of peoples in the ancient archipelago.

However, it likely took over a millennium for the Japanese language to become systematically structured in its modern form. One significant evidence for this is the existence of the Japanese phonetic chart called the Gojuon (“五十音図,” literally “Fifty-sound Chart”). The originator and exact period of creation of the Gojuon remain shrouded in mystery, but the earliest development arose from Japan initially lacking a native phonetic script. This led to the invention of Man’yogana (“万葉仮名”), a phonetic notation using borrowed Chinese characters to represent Japanese sounds. This innovation significantly contributed to classical texts such as the Kojiki (712 CE) and Nihon Shoki (720 CE), though this literary culture fully blossomed later in the Heian period.

During this era, noble courtiers, Buddhist monks, and Shinto priests regarded literacy as a cornerstone of education. Dissatisfied with the traditional method of using borrowed Chinese characters to represent Japanese sounds, they developed the cursive-styled “Hiragana” (“平仮名”) derived from Man’yogana, and the simplified “Katakana” (“片仮名”) based on components of Chinese characters. These new kana scripts (“仮名”) represented an intentional shift away from dependence on Chinese characters, resulting in the establishment of Japan’s unique kana writing system. In the process of kana adoption, ambitious attempts to systematically organize Japanese phonetic syllables emerged.

This development was partly influenced by studies of Chinese phonology and rhyme books imported from China. From the Nara to Heian periods, composing Chinese poetry became popular in Japan, introducing rhyme tables known as “Inchu-zu” (“韻紐図”), diagrams arranging characters horizontally and vertically based on shared phonetic features. Under this influence, Japanese waka poets began to recognize similarities among syllables sharing the same vowels, thus fostering the idea of systematically organizing Japanese syllables based on consonant-vowel structures. In other words, the strong influence from Chinese phonological studies led Japanese scholars, for the first time, to recognize vowels as central to their phonological system.

Furthermore, the introduction of Sanskrit phonology—known as Shittan-gaku (“悉曇学”)—accompanying the arrival of Buddhism significantly contributed to the establishment of the Gojuon. Influential monks of the early Heian period, such as Kukai (774–835), founder of Shingon Buddhism, and Ennin (794–864) of the Tendai sect, traveled to Tang China to learn the Siddham script and Sanskrit phonetic systems. The Siddham script systematically arranged vowels and consonants, an Indian-origin phonetic theory that Kukai and others brought to Japan. Thus, during this period, Japanese scholars came into academic contact with an entirely different linguistic tradition through India.

Indeed, the earliest known Japanese phonological table, annotated within the Heian-period Buddhist manuscript Kujakukyo Ongi (“孔雀経音義”), is considered the prototype of the Gojuon. Therefore, by the mid-Heian period, phonetic principles derived from Sanskrit phonology were adapted to Japanese kana, leading to the creation of an organized framework for kana syllables.

However, at this stage, the term “Gojuon” had not yet emerged, and this knowledge was restricted to a limited circle of scholars, preventing Japanese from achieving full systematization. When, then, did this closed situation finally change? A crucial turning point was the Edo-period scholarly movement known as Kokugaku (“国学,” literally “national studies”), a topic that has previously been explored several times on Shitsurae.