一般而言，作為一項教學技術的建構主義，可分為個人的或激進的建構主義以及社會的建構主義，分別以E. von Glasersfeld 及Gergen 為代表學者。本文將探討這兩個理論所根據的知識論系統是什麼？知識成立的有效性立場又是什麼？討論這個主題，同時提出研究者的論辯，不論是個人或是社會建構主義都可以藉由維根斯坦晚期哲學，釐清兩者，並在理論上彰顯出兩者在知識的看法上仍未能脫離傳統知識的實在論基礎。按照von Glasersfeld 提出的理論，知識是屬於個人的經驗，而且不可能有客觀實體作為知識的基礎，知識只借助於其是否適合（fit）的原則，這與只承認屬於自己的知識說法一樣。那麼，我們如何得知他人擁有的知識呢？在維根斯坦的討論中，這是不可能的，因為我們無法根據私人語言獲得任何知識。Gergen 的理論，只以語言作為知識建構的媒介，不能創造事實。研究者的論辯是知識的建構主義只能說在解釋上可以依據不同的個人經驗或社區關係而有不同的知識理論，但是在其解釋的背後，仍需要有實在事實現象或對象為本。

In this paper, I will discuss the philosophical foundation of individualistic or radical constructivism and social constructivism with E. von Glasersfeld and K. J. Gergen as their leading scholars respectively. The main questions discussed are what their epistemological systems are, and what their philosophical foundation would be. I will argue that both theories still have to base on realism in terms of traditional epistemology. When applying ‘fit’ principle of radical constructivism, we can only apply personal experience in various situations for explanation and for creating our own meanings, but are unable to alter the fact which is open to everyone for different explanations. Based on Wittgenstein’s viewpoint, neither theory is able to rid of the realistic view of knowledge. Also, according to Wittgenstein’s later philosophy, it is not possible to create knowledge by personal language, since language cannot be the media of constructing knowledge and cannot create fact either.