Within constructivist theory, knowledge isn't something that exists outside of the learner. According to Tobin and Tippins (1993), constructivism is a form of realism where reality can only be known in a personal and subjective way. Von Glasersfeld notes that constructivist theory acknowledges reality but he goes on to say, "I define to exist only within the realm of our experiential world and not ontologically…" (Tobin, 1993, p. 4). While constructivism takes on different philosophical meanings with different theorists and contexts, the over arching concept hinges itself upon the nature of knowing and the active role of the learner.