學者們對「四十二字門」的原意是為幫助記憶和宣傳佛教教義的看法，大體上一致. 但對其來源，學者們 則有：1. 中亞說，2. 西北印度說，3. 印度本土說等三種看法. 筆者認為﹕從語言的特點和佛教經典形成的過程來看，「四十二字門」最早形成於西北印度的可能性很大，但使用「字門」作為表達，誦讀，記憶經典的方法在印度本土或在梵文文獻中也早有傳統. 英國劍橋大學的教授J.Brough首先發現﹕西晉竺法護譯《普曜經》講到「四十二字門」時，在每一條的開首，舉列不是「字」，而是「詞」. 這在所有講到「四十二字門」的經典中，是最為特殊的，或可以說絕無僅有. 中國南北朝時代慧思曾有《四十二字門義》的著作，可惜這部書大概唐以後佚失了. 此外，清代的《同文韻統》之「大藏經字母同異譜」，根據十三種佛經，排列出一個梵字的對照表，其中九種都是出自「四十二字門」. 「四十二字門」與《悉曇章》沒直接的關係. 但「四十二字門」的四十二個梵字，既然一開始就被稱作「陀鄰尼目佉」，實際上成一套咒語，不僅念誦，也可書寫，當然也就被認為是悉曇的一種. 尤其是唐代，佛教的密宗和悉曇都盛行，二者互相結合，文人學士，士大夫等也常常以能書寫悉曇字為時尚. Scholars agree that "the 42 (arapacana) Syllabary" was designed to assist memory and to help spread Buddhism.However，there is disagreement as to the source of this alphabet，assigning it to Central Asia, northwestern India, or India proper. I believe that examination of its linguistic properties and the conception of Buddhist texts indicates northwestern India as the most probably source.However，using "Syllabary (Letter Doors)" to express,recite，and remember texts has a long tradition in India proper and in Sanskrit literature. Professor J. Brough of Cambridge in England was the first to notice that when Zhufahu (Western Jin Dynasty，239~316 A.D.)mentioned the 42 Syllabary in his translation of the Puyao Sutra, at the beginning of each section he did not provide letters, but words. This is unique among all texts concerning the 42 Syllabary. During the South and North Dynasties (5th and 6th centuries A.D.),Hui-shi wrote An Exposition on the Meaning of the 42 Syllabary; unfortunately，this work was lost sometime after the T'ang Dynasty. The Qing Dynasty Unified Rhymes (Tongwen Yuntong) includes charts comparing the letters recorded in the Canon. These charts compare the letters listed in thirteen sutras; nine of these alphabets are of 42 letters. However，the 42 Syllabary is not directly related to the Siddham alphabet.Nonetheless, the 42 letters begin with DHA-RA-NI-MU-KHa,which actually can function as a mantra, so the letters may not only be recited，but also written，so of course they were considered a type of Siddham. Especially during the T'ang Dynasty，when both Tantric and Siddham practices flourished，they influenced each other，and the ability to write Siddham letters was prized among the fashionable gentry.
