stantiating evidence to be found in contemporary or slightly later sources. The former he called "internal evidence" (pên-chêng 本證), and the latter "external evidence" (p'ang-chêng 旁證). What his predecessors in the T'ang and Sung periods had vaguely called "rhyme by poetical license" (叶韻) he showed to be a fiction, and demonstrated, moreover, that the ancient rhyming system could be recovered with a reasonable degree of certainty.
Ku Yen-wu adopted Ch'ên's method in his own more extensive phonetical researches and, by adducing still more examples to show its applicability, he so popularized it that it became one of the most effective tools of Ch'ing scholarship. Without it many later examples of exacting philological and historical research would have been impossible. The great scholars, Tai Chên, Ch'ien Ta-hsin, Tuan Yü-ts'ai, Wang Nien-sun [qq. v.] and Chiang Yu-kao 江有誥 (T. 晉三, H. 古愚) used it successfully in their further researches in phonetics and etymology, as did Yen Jo-chü and Ts'ui Shu [qq. v.] in the field of historical criticism and in determining the authenticity of ancient texts. This combination of historical research and textual criticism with the use of inductive reasoning, marked the highest attainment of scholarship in the Ch'ing period.
Ku Yen-wu's application of the method initiated by Ch'ên is found in his 音學五書 Yin-hsüeh wu-shu, which comprises five works on phonetics, printed in 1667 at Shan-yang, Kiangsu, with the assistance of Chang Shao 張弨 (T. 立臣, H. 丞齋, 1625–1694). The individual titles are: 音論 Yin-lun, 3 chüan, a general discussion; 詩本音 Shih pên-yin, 10 chüan, on the rhymes in the Classic of Poetry; 易音 I-yin, 3 chüan, on the rhymes in the Classic of Changes; 唐韻正 T'ang yün chêng, 20 chüan, a comparison of the sounds in antiquity with those of the T'ang period; and 古音表 Ku-yin piao, 2 chüan, a table of the sounds in antiquity.
But the work by which Ku Yen-wu is most generally known is his collection of carefully written notes on a great variety of topics, entitled 日知錄 Jih-chih lu—first printed by him in 8 chüan in 1670. After many revisions and amplifications it was edited by P'an Lei and printed in Fukien in 1695 in its present form of 32 chüan. The notes are the result of thirty years of wide and thoughtful reading and on the observations he made in the course of his long journeys on horseback. Not one of these notes, he says, was written without long meditation, and many of them were revised again and again. The 32 chüan edition may roughly be separated into the following topics: chüan 1–7 on the Classics; 8–12 on government and economics; 13–15 on ethics and social relations; 16–19 on the civil service examinations and the writing of essays; and 20–32 on literary, historical and philological matters. The second edition was an improvement over the first, owing in part to alterations suggested by various scholars, particularly by Yen Jo-chü. Other alterations were made in order not to offend the susceptibilities of Manchu rulers. A modern scholar, Huang K'an 黃侃 (T. 季剛, 1886–1936) compared the 1695 edition with an old manuscript and published his collation notes in 1933 under the title, Jih-chih lu chiao-chi (校記), indicating at the same time the alterations that were made by P'an Lei. An edition of the Jih-chih lu, published in 1795, contains 4 chüan of supplementary notes not included in the edition of 1695. The edition now most popular is one printed in 1834 by Huang Ju-ch'êng 黃汝成 (T. 庸玉, H. 潛夫, 1799–1837), with annotations by various scholars. Since then Li Yü-sui (see under Li Fu-sun), Yü Yüeh and Ting Yen [qq. v.] have made valuable additions or emendations of their own.
In the field of geography Ku Yen-wu has three extensive works to his credit. One, bearing the title 肇域志 Chao-yü chih, is a compendium of historical geography rather similar to the Tu-shih fang-yü chi-yao of Ku Tsu-yü [q. v.]. It was never printed, but two incomplete manuscript portions are preserved in the Kuo-hsüeh Library, Nanking. Some indication of the scope of the work can be gained from a statement in the preface which reads, "First I drew on the general gazetteers of the empire; next on the provincial, departmental, and district chronicles; and finally on the Twenty-one Dynastic Histories. In all I consulted more than one thousand works". His second work in which he laid stress on plans of strategic military importance, on taxation, on waterways, is entitled 天下郡國利病書 T'ien-hsia chün-kuo li-ping shu. Like the work just mentioned, this compilation was begun in 1639; the preface was written in 1662. A poorly printed edition of it, separated into 120 chüan, was produced by Lung Wan-yu 龍萬育 (T. 爕堂) in Szechwan in 1811 with a revision to 1823, and this is the print most generally known. But fortunately the original draft, partly in Ku Yen-wu's own hand, was reproduced in 1936 in the third series of the 四部叢刊 Ssŭ-pu ts'ung-k'an. Ku's third topographical study, entitled
424
