It should be remembered that what remains today in writing of the pre-Qin schools should not necessarily be considered representative of their relative importance at the time. During the warring states period, Mencius complained that the world was full of the words of Mozi and Yangzi; yet today little remains of Yangzi’s doctrines, and much of the book of Mozi survived only by historical accident. Similarly, Huizi was a debater whose ideas had considerable influence on debate at the time (as is recorded in the Zhuangzi and other texts), yet no works of his remain extant today. History played a large part in ensuring the preservation of the Confucian texts, as well as the various ancient classics revered by the school, and perhaps also the various Legalist texts.
Additionally, attention should be paid to the way texts were prepared and handed down through the ages. Many texts of the period claim to either be the work of or record the words of a particular scholar or historical person of the time. However it is often difficult to establish the authenticity of these attributions, and in some cases they are simply not true. In many cases, works were prepared largely by the followers of a particular school of thought, and a single book may be the collective work of many authors, sometimes over a period of decades or even hundreds of years. Naturally, this means that events and conversations recorded in one book (by one school of thought) are prone to bias, and tend to present their own side in a positive light; debates between opposing thinkers often end with one side appearing “lost for words” and accepting defeat, when in reality they might well have had much more to say; in some cases, historical figures are presented as caricatures or figures of ridicule.
Because texts were generally reproduced by scribes copying the original text character by character, the transmission of texts could easily introduce accidental errors; occasionally, new passages were inserted and presented as part of the original work. The compactness and flexibility of classical Chinese made it quite possible to accidentally skip or repeat an entire column of text without being alerted to the error by grammatical rules. A scribe might consciously or unconsciously substitute an alternative form for a character, perhaps because the existing form had become obsolete, or even substitute an entirely different character of similar meaning, so as to avoid the use of a forbidden character (such as a character used in the name of the current emperor). For these reasons it is generally impossible to date precisely a work of the period, and in the cases of many texts there are ongoing debates about which chapters should be considered representative of their supposed author, and from which period each originally dates.