本文透過思與知言的兩個概念來省察孟子對適德有效性之構想。孟子的整個道德哲學一貫地說明的，不外是道德的正當根據以及其正當根據如何有效地實現到客觀世界為中心內容。並且，孟子的這種構想是從兩個前提上出發的。其一，人類是道德的，因為作為可自我完善的存在物。他們不可能僅僅是受生存的本能需要，也不僅僅是受維持社會穩定的種種必要性所制約。第二，人雖然是一個道德的存在，也不可避免地是生物的、心理的、社會的存在，因此為了實現自己，他們必須把這些限制改變成自我發展的必要媒介。 如此，從這兩個前提上看，首先要成為人應當成為的樣子，就必須從日常的反求諸己，即自我反省開始。儘管社會環境與心理條件在人的成長中起重要的作用，但這些並不能成為建構適德之根本根據。道筏並不是由學習而內化的，而是經過學習而表現出來的。所以在孟子道德哲學中，學習或對客觀世界之認識，被看成是內在道德與歷史、社會條件的相互滋養之通路，而不是把外在價值強加給無教養的心靈。

　　　　　This paper gives an account of Mencius' conception of the validity of morality through the two concepts of ssu and chih-yen. What Mencian moral philosophy explains constantly is the legitimate ground of morality and how this legitimacy could be realized in the objective world. This conception is based on two assumptions. First, human beings are moral beings, and because they are self-perfecting beings, they could not be merely subjected to the instinctive need of survival, nor the conditioning of the necessities of social maintenance. Second, though human beings are moral beings, they are also biological, psychological and social existence, and to realize themselves, they have to transform these limitations into the medium for self realization.Thus, from these two assumptions, human beings have first to be what a human being should be, and start by self reflection (ssu) in daily affairs. Though social environment and psychological conditions bear important functions in one's growth, these could not be the ground of moral construction. Morality is not internalization through learning, but manifests through learning. Hence, in the view of Mencian moral philosophy, learning or knowing the objective world (chih-yen) is regarded as the way of interaction and sustaining of inner morality with the historical and social conditions, rather than the inculcation of external value onto the natural mind.