晏斯盛（字虞際，號一齋，？ -1752）為清中葉《易》學家，強調《易》 為聖人藉卜筮以明義理之書，主張即《易》以明象言理，並以一陰一陽的易簡 思想為《易》的核心義理。晏氏以成卦原則及成卦後原則的二重區分論通例， 成卦原則據〈繫辭傳〉肯定重卦說，據〈雜卦說〉談反對卦變；成卦之後，自 然可就六畫卦作整體考察。後人對晏氏《易》著體例提出三點批評：一、擅自 於六十四卦各爻爻辭前畫一全卦而間以一動爻；二、割裂傳文以附經文；三、 重新編排《十翼》篇目次第的用意無法理解。然這三點實與晏氏視《易》為卜 筮之書及欲羽翼《易》經傳的理念有關。釋象作法主張不可悖逆卦義，並據《易 傳》釋象，且並非全面釋卦爻辭取象。義理釋《易》的重心在發揮陰陽之理， 據《易傳》一陰一陽、乾元、易簡、時、幾等概念加以融貫，建立獨特的易簡 哲學，發揮《易》重視時變的特性。此外晏氏《易》學與程廷祚（字啟生，號 錦莊，1691-1767）《易》學有相近及相異處，可相互對照研究。

Yan Si-Sheng is a mid-Qing scholar of the Classic of Changes who emphasizes that the Classic of Changes is a book of fortune-telling with which sages explain moralities. Yan advocates that one should explain the reasons behind phenomena with the Classic of Changes, and that the simplified thought of yin and yang is the core principle of the Classic of Changes. Yan distinguishes the principles of forming hexagrams from the principles after forming hexagrams. His principles of forming hexagram affirm the Xicizhuan’s formulation of double trigrams and oppose the Zaguashuo’s hexagram alternation. He thinks that one can observe the hexagram after forming one. Later scholars criticize Yan’s principles for the following three reasons: 1. Yan draws a whole hexagram before every line-explanation of the sixtyfour hexagrams, and inserts a variable yao in it at his will. 2. Yan takes sections of the Commentary of the Classic of Changes out of its context to fit in the Classic of Changes. 3. Yan rearranges the order of the Ten Wings, the purpose of which is not understandable. These are in fact because Yan regards the Classic of Changes as a fortune-telling book and intends to support the ideas of the Classic of Changes and its Commentary. Yan believes that one should not explain phenomena against the meaning of the hexagram because of the Commentary or take the hexagram-line explanations as a whole to explain phenomena. He thinks the Classic of Changes should be interpreted by realizing the principles of yin-yang. Thus he integrates the concepts of yin-yang, qian-yuan, simplicity, time, and timing according to the Commentary and constructs his unique philosophy of simplicity that displays the importance of timing changes in the Classic of Changes. Yan’s doctrine of the Classic can be compared to Cheng Ting-Zuo’s for their similarities and dissimilarities.