 Antoine Arnauld develops an account of reflection that incorporates this distinction. The reflection that is essential to any thought does not involve a second order perception. As noted above, Arnauld argued that each thought has reflection built into it, although this does not entail a second-order thought. Only explicit reflection, where an individual focuses their attention on their own thoughts, requires a second-order perception. (For more on Arnauld’s account, see Nadler 1989, 118–22.)