In his last commentary—called the Long Commentary —he proposes another theory, which becomes known as the theory of "the unity of the intellect ". In it, Averroes argues that there is only one material intellect, which is the same for all humans and is unmixed with human body. To explain how different individuals can have different thoughts, he uses a concept he calls fikr —known as cogitatio in Latin—a process that happens in human brains and contains not universal knowledge but "active consideration of particular things" the person has encountered. This theory attracted controversy when Averroes's works entered Christian Europe; in 1229 Thomas Aquinas wrote a detailed critique titled On the Unity of the Intellect against the Averroists.