Aquinas's interpretation of EN 3.1-5 reveals from the outset a special interest in "choice". He states explicitly that Aristotle's definition of virtue as a "habit issuing in choices" requires a special treatment. The other main concepts discussed in 3.1-5, "the voluntary" and "the will" are in Aquinas's view connected with choice. Since choice is an interior act of the will, it is free in the sense of not being necessitated by any factor outside human reason, and cannot be impeded from taking place. It is thus the act about whose freedom there can never be any doubt. Aquinas's concept of will is not confined to simply positing a "rational appetite". By integrating an Augustinian concept of interior freedom and Aristotelian philosophy of nature, Aquinas is able not only to affirm that the will is open to alternative courses of action but to interpret this as a natural phenomenon.