During Later Han Dynasty, when orthodox Confucianism was already established as the leading school of state thinking and interpreting the traditional classical writings, it was necessary to make exact definitions for terms occurring in the writings of old times. Terms were to be interpreted by the way the New Text School saw the classical writings, Confucius being an uncrowned king and a holy treasurer of tradition and ritual conventions. Another reason to define terms and to fix the writing process was the standardisation of characters during the Qin and Han Dynasties. Han time "modern" characters were sometimes very different the old writing characters (guwen 古文), the Large Seal (dazhuan 大篆 or zhouwen 籀文) and the Qin time Small Seal script (xiaozhuan 小篆). The largest compendium for Chinese characters is the book "Explaining simple and analyzing compound characters" written by Xu Shen 許慎 (d. 147 AD). He divided the whole corpus of Chinese characters into 540 classifiers (also called determinants or radicals, in Chinese bushou 部首) like man 人, wood 木, water 水, soil 土, and so on, some of them are standing alone, without building compounded characters, like five 五, six 六 and seven 七. Many of these 540 classifiers are viewed as part of other groups today (the Shuowen lists 箕 as a classifier, today it is subsumed under bamboo 竹).
The main commentator of the Shuowen is Xu Xuan 徐鉉 (d. 991), who added the pronunciation parts according to the "reverse cutting" system (fanqie 反切), using the initial sound and the final sound of two words/characters to describe the sound of a word/character.
Xu Shen distinguishes between six kinds of characters (liushu 六書):

• xiangxing 象形: "depicting the shape", pictures of concrete things or abstract things like a sun 日, eyebrow 眉 (eye 目 and brow ), exchange 交 (old: ; two crossed legs), and a board 片 (old: ; half of a tree 木, old: ).
• zhishi 指事 (also called chushi 處事 or xiangshi 象事): "pointing at situations" ("placing situations" or "depicting situations"), marking a character with a dot or a stroke to indicate a part of it like "above" 上, the blade of a knife 刃, the root of a tree 本 or "deficient" 乏 (a "correct" 正 turned upside down; old: ).
• huiyi 會意 (also called xiangyi 象意): "combining meanings" ("depicting meanings"), image of an abstract sense like dawn 旦 (the sun over the horizon), public 公 (opening 八 a market place ㄙ), trusting 信 (a man 人 speaking 言), or bright 明 (sun 日 and moon 月). Sometimes one of the parts is abridged, like "lame, slow" 蹇 足 "foot" and 寒 "cold", leaving out the two dots.
• zhuanzhu 轉注: "mutually interpretation (tautology)", creating a new character an old one to differ between words with the same meaning but with slightly different pronunciation, like "old" 老 lao and "aged" 考 kao, "give back" 返 fan and "turn back" 還 huan, or "tip of a branch" 標 biao and "end of a stalk" 杪 miao. A rare type.
• jiajie 假借: "false borrowing", borrowing a character for a word that is pronounced equally but has a totally different meaning, like 我 (a kind of axe 戈) for "me", or 來 (a kind of grain; modern form 麥) for "coming". The characters are only used in their new sense since the Spring and Autumn period. Many grammatical particles without particular meaning are of this type, making it necessary to create a new character for the original meaning: 乃 nai "breast", borrowed for nai "therefore", creating the new character 奶 for "breast, milk" with the determinant 女 "woman"; or 其 qi "basket", borrowed for qi "his, her, its", creating the new character 箕 (modern pronunciation ji) for "basket" with the determinant 竹 "bamboo". The character 之 zhi originally means "to go", but it is also used as a genetive particle, an object pronoun and sometimes as demonstrative pronoun "this", without having lost its original meaning. This kind of character shows that Chinese characters could also be used only with their sound, thus creating a kind of syllable script.
• xingsheng 形聲 (also called xiesheng 諧聲 or xiangsheng 象聲): "shape and sound" ("harmonizing with sound" or "picture and sound"), a combination of a classifier (sphere of word sense) and a sound, like "pear" li 梨 木 "tree" and 利 li, or "controlling" zhang 掌 手 "hand" and 尚 shang. Some of the phonetic parts are also used with their true meaning, like "the middle of three" zhong 仲 人 "man" and 中 zhong "middle", or the character set of 包 bao "package": 苞 bao "bud" (with 艸 "grass"), 胞 bao "placenta" (with 肉 "flesh"), 雹 bao "hail" (with 雨 "rain"), 飽 bao "full stomach" (with 食 "to eat"), 抱 bao "to embrace" (with 手 "hand"), 泡 pao "foam" (with 水 "water"). This type is the most widespread.

In the following examples, old types are green, and Large Seal Script characters are red.

１上．【一】惟初太始道立於一。造分天地，化成萬物。凡一之屬皆從一。於悉切。【弌】古文一。
1A. Unity 一: It is, that the start of the Great Begin of the Way is based upon Unity. It divides Heaven and Earth and forms the ten thousand creations. All things related to "one" have the 一 as part of the character (元、天、丕、吏). Pronounced like Y- and -I (yi). 弌 is an old character for 一.
【】顛也。至高無上。從一、大。他前切。
Heaven 天 (tian): is the summit (dian). The highest point where nothing can mount above. The character is compounded of "one" and "great". Prounounced like T- and -IAN (tian).
【】高也。此古文上。指事也。凡上之屬皆從上。時掌切。【】篆文上。
Above 上: is high. It is the old character for 上, character type "pointing to situation". All things related to "above" have the 上 as part of their character (帝、旁、下). Pronounced like SH- and -ANG (shang). is the Small Seal script character for 上.
【】諦也。王天下之號也。從上、朿聲。都計切。【】古文帝。古文諸上字皆從一，篆文皆從二。【二】古文上字。辛、示、辰、龍、童、音、章，皆從古文上。
Emperor 帝 (di): is careful (di). Denomination for the true ruler of the earth. Deriving "above" and the sound of 朿 ce or qi. Pronounced like D- and I (di). is an old character for 帝. All old style characters with the radical 上 are written with a simple stroke 一, the Small Seal style characters with a double stroke 二. 二 is an old character for 上. The following characters are written with the old style 上: xin (a celestial stem), shi (showing), chen (an earthly branch), long (dragon), tong (young), yin (sound) and zhang (stanza).
８上．【】天地之性最貴者也。此籀文象臂脛之形。凡人之屬皆從人。如鄰切。
8A.Man 人: the worthiest of all the beings between Heaven and Earth. This is the Large Seal character depicting of a man with arms and legs. All things related to man have the 人 as part of their character. Pronounced like R- and -IN (ren).
【】考也。七十曰老。從人、毛、匕，言鬚髮變白也。凡老之屬皆從老。盧皓切。
Old 老: aged. Seventy years is old. Compounded of the characters for man, hair and change, saying that beard and hair becoming white. All things related to old age have the 老 as part of their character (like 耆、壽、孝). Pronounced like L- and -AO (lao).
【】老也。從老省、ㄎ聲。苦浩切。
Aged 考: old. Compounded of an abridged 老 and the sound of ㄎ kao. Pronounced like K- and -AO (kao).
１３下．【土】地之吐生物者也。二象地之下，地之中物出形也。凡土之屬皆從土。它魯切。
13B. Soil 土: what the earth produces of living creatures. The two horizontal strokes depict the earth below, (and the vertical stroke) depicts what beings come out of the earth. All things related to earth have the 土 as part of their character. Pronounced like "T" and "U" (tu).
【】元氣初分輕清陽為天，重濁陰為地。萬物所陳列也。從土、也聲。徒內切。【】籀文地，從隊。
Earth 地: The prime breath divided the light, clear and bright things as Heaven the heavy, muddy and dark things as Earth. It is that what arranged the ten thousand beings. Deriving "soil" and the sound of 也 ye. Pronounced like T- and -EI (di). is a Large Seal style character for 地, derived 隊.
【】東方之孟陽氣萌動，從木戴孚甲之象。一曰：人頭空為甲。甲象人頭。凡甲之屬皆從甲。古狎切。【】古文甲，始於十，見於千，成於木之象。
Shield, or the first of the Celestial Stems 甲: When the first sun breathes the east, the sprouts move out of the earth. The character depicts a wooden handle headed with a trustful shield.Somebody states, using a hollow skull as shield, the character depicting a man's head. All things related to shield have the 甲 as part of their character (actually none). Pronounced like G- and -IA (jia). is an old character for 甲, depicting: Beginning with ten, becoming apparent with thousand, completed in a tree.
【】十一月陽氣動萬物，滋人以為偁。象形。凡子之屬皆從子。李陽冰曰：子在中足併也。即里切。【】古文子，從川象髮也。【】籀文子，囟有髮臂脛在几上也。
Son, or the first of the Terrestrial Branches 子: In the eleventh month, the sun breath moves the ten thousand beings, nourishing man to full accordance with nature. The character is a picture (of a child). All things related to children have the 子 as part of their character (like 孕、字、孿、孺、季、孟、孽、孳、孤、存、疑). Li Yangbing says: It depicts a baby in its diapers, the feet side by side. Pronounced like J- and -I (zi). is an old character for 子, three strokes depicting the hair. is the Large Seal script character, the fontanel having hair, arms and legs and lying on a small table.