 As Geneviève Lewis shows, this issue became a critical source of debate in the later seventeenth century. She notes that Pierre-Silvain Régis, in his defense of Cartesianism, commits himself to some sort of reflective knowledge as a constitutive part of consciousness. Régis, like Arnauld, reaches all the way back to Augustine as a source for this doctrine, quoting Augustine’s claim that “it is necessary that [an animal] perceives (sentio) that it does see when it sees” (Augustine 37, quoted by Régis, Système I, 150) When conscious of something, one “perceives that one perceives it.” This way of putting it was actually quite common as a way of describing the psychological sense of consciousness—one not only sees a red ball, but one also perceives that one perceives the red ball. This sounds for all the world like a reflective act.