李德懋는 조선후기 博學으로 널리 알려진 학자이다. 그의 박학적 면모는 30대 이후 보이는 고증학적 성향이 농후한 저술에서 확인된다. 그리고 이러한 이덕무의 학문 성향은 청대고증학의 영향으로 이해되어 왔다. 그러나 과연 그러한가? 이덕무는 20대 중반에 청대고증학자 黃宗羲를 접했고, 30대 전후하여 고증학자들의 서적을 열독하였으며, 30대 중반 이후의 저술에 적극 활용함을 확인할 수 있었다. 따라서 이덕무가 청대고증학에 큰 관심을 가졌고, 그들로부터 영향 받았음은 틀림없다. 하지만 이덕무가 접한 청대고증학자는 黃宗羲, 顧炎武, 毛奇齡, 朱彛尊, 徐乾學으로, 이들은 청대 초기 고증학 형성기에 활동한 학자들이다. 청대고증학의 전성기에 활동한 戴震, 錢大昕, 章學成 등에 대한 언급은 그의 문집 어디서도 찾아볼 수가 없다. 이덕무는 청대고증학 전체의 흐름을 꿰뚫을 수 있는 입장은 아니었고, 다만 청대 초기 고증학의 일부만을 접하고 수용할 수 있었다.
이덕무는 청대고증학자 중 顧炎武의 영향을 가장 많이 받았다고 알려져 있다. 하지만 이덕무가 열독한 서목과 인용한 내용을 통해 모기령, 주이준, 서건학 등의 영향도 적지 않았음을 확인할 수 있다. 그런데 이들 학자들은 학문적 지향과 삶의 행적이 판이하다. 顧炎武가 대명의리를 지킨 절의의 인물이자 주자 학문을 옹호하는 측면이 강했던 반면, 毛奇齡은 청에 벼슬한 이력이 있을 뿐만 아니라 대명의리를 지킨 인물을 논박하기까지 했으며, 주자를 철저히 비판한 반주자학자였다. 이덕무는 대명의리와 주자 옹호적 입장을 중시했음에도 불구하고 모기령과 주이준의 박학과 고증학적 학문방법을 대단히 높이 평가하였다. 이는 이덕무가 청대고증학을 수용함에 있어서 ‘치밀한 考據를 바탕으로 한 考證學的 학문방법’을 중요시했음을 의미하는 것이라 하겠다.
이덕무는 유년시절부터 名物學에 대한 관심이 지대했고, 考據?辨證을 중요시 하는 학문 자세를 지녔으며, 20대 시절에는 鄭樵와 馬端臨을 본받아 백과사전식 類書를 만들고자 기획하기도 했다. 이는 이덕무가 청대고증학을 접하기 이전에 이미 名物度數學에의 깊은 관심과 고거?변증하는 학문방법을 가지고 있었음을 말해준다. 그리고 이덕무는 30대 전후하여 청대고증학을 수용하면서 특히 고증학적 학문방법에 깊은 공감을 보였는데, 이는 이덕무가 평소 지향하던 博學과 考據?辨證의 학문방법과 잘 맞아떨어졌기 때문일 것이다. 따라서 이덕무 학문의 고증학적 성향은 청대고증학의 수용만으로 이해하기 보다는, 타고난 꼼꼼함과 유년시절부터 지니고 있던 명물도수학에의 관심과 고거?변증을 좋아하던 성향이 청대고증학의 수용과 결합되어 나온 결과라 이해하는 것이 타당할 것이다.
Lee Deok-Mu is a scholar well known for erudition in the late Joseon period. His erudite aspect is identified in his writings with a strong documental archaeological tendency in his 30s and thereafter. Lee Deok- Mu's academic tendency as such has been understood as a result of the effects of Qing Dynasty Period documental archaeology. However, is it really so? Lee Deok-Mu encountered Hwang Jon-Hee, a scholar specialized in Qing Dynasty Period documental archaeology in his mid-20s and enthusiastically read the books of scholars specialized in Qing Dynasty Period documental archaeology including Goh Yeom-Mu and cited the contents in his writings in his mid-30s thereafter. Therefore, the fact that Lee Deok-Mu was greatly interested in Qing Dynasty Period documental archaeology and enthusiastically read the books of scholars specialized in Qing Dynasty Period documental archaeology is indisputable. However, scholars specialized in Qing Dynasty Period documental archaeology encountered by Lee Deok-Mu were Hwang Jong-Hee, Goh Yeom-Mu, Mo Gi-Ryeong, Ju Ee- Jun, and Seo Geon-Hak who acted in the early part of the Qing Dynasty Period when documental archaeology was being formed. Mentions about Dae Jin, Jeon Dae-Heun, and Jang Hak-Seong who acted in the prime of documental archaeology in the Qing Dynasty Period cannot be found anywhere in the collection of his works. Given Lee Deok-Mu's birth and death date, it is natural that the documental archaeology accessed by Lee Deok-Mu is part of the documental archaeology during the period of Qianlong in the early part of the Qing Dynasty Period. Therefore, although Lee Deok-Mu was greatly interested in Qing Dynasty Period documental archaeology and wanted to obtain and read the books of scholars specialized in Qing Dynasty Period documental archaeology, he was not in a position to completely understand the stream of the entire Qing Dynasty Period documental archaeology but could accommodate only part of the documental archaeology at the beginning of Qing Dynasty Period.
Lee Deok-Mu is known to have been affected the most by Goh Yeom-Mu among scholars specialized in Qing Dynasty Period documental archaeology. However, though the titles of books enthusiastically read by Lee Deok-Mu and the contents cited by them, it could be identified that the effects of Mo Gi-Ryeong, Ju Ee-Jun, and Seo Geon-Hak were not small. However, the academic orientation and course of life of Goh Yeom-Mu /Seo Geon- Hak and those of Mo Gi-Ryeong/Ju Ee-Jun are completely different. Whereas Goh Yeom-Mu was royal to Ming Dynasty and strongly advocated neo- Confucianism, Mo Gi-Ryeong not only had been in government service for Qing Dynasty but also argued against those who were royal to Ming Dynasty and thoroughly criticized Chutzu. Despite that Lee Deok-Mu was royal to Ming Dynasty and regarded the position of advocating Chutzu as being important, he evaluated highly, the erudition and documental archaeological academic methods of Mo Gi-Ryeong and Ju Ee-Jun. This should mean that when Lee Deok-Mu was accommodating Qing Dynasty Period documental archaeology, he regarded important, the ‘documental archaeological academic methods based on elaborate historical evidence.’ It is said that Lee Deok-Mu had a habit to think over history for notes and seek for historical evidence for doubtful contents from when he was young, had wide knowledge as he read diverse books, in particular, had profound knowledge of studies of grass and trees, birds and beasts, mountains and rivers, and customs, and carefully sought for historical evidence and demonstrated when he was writing books. He planned to write encyclopedic books such as <Tongji> of Jeong Cho and, <Munheontonggo> of Ma Dan-Rim when he was young. Through this, it can be seen that Lee Deok-Mu already had deep interest in and affected by speciality studies before he encountered Qing Dynasty Perioddocumental archaeology. When he was accommodating Qing Dynasty Period documental archaeology in his 30s, Lee Deok-Mu deeply sympathized with documental archaeological methods in particular probably because these methods were well consistent with erudition and the academic methods of seeking historical evidence and demonstrating that he pursued at normal times. Therefore, the documental archaeological tendency of Lee Deok-Mu's studies should be understood as a results from the combination of his meticulousness and tendency toward seeking historical evidence and demonstrating that he had from when he was young and his accommodation of Qing Dynasty Period documental archaeology rather than just a result of accommodation of Qing Dynasty Period documental archaeology.