For him, the possibility of understanding rests on the relationship between intellect and sense perception. Aristotle's remarks on the concept of what came to be called the "active intellect" and "passive intellect" (along with various other terms) are amongst "the most intensely studied sentences in the history of philosophy".[26] The terms are derived from a single passage in Aristotle's De Anima, Book III. Following is the translation of one of those passages[27] with some key Greek words shown in square brackets.