Choice and deliberation are not outside activity for Aristotle, rather they are internal to it. Choice means performing a certain act, and deliberation is linked to the possibilities that the situation offers to me, rather than what I might think would be the best. Again this is the recognition of the limits of human action. Sometimes the situation is so difficult that I might need to perform an act that in other circumstances I would never think of doing because it is the situation itself that demands it. It is for this reason, Aristotle argues, that we need to distinguish between practical and scientific reason .
Scientific reason is suitable only to what is governed by laws that are universal.
Again this is the great difference between Plato and Aristotle. Plato only saw one kind of knowledge, universal science, which was applicable in the same way both to the mathematical objects, as it was to human conduct. Aristotle, on the contrary, would say that to concern oneself with generalities would be to think one could have moral laws in the same way that one could have mathematical and scientific laws, would be to do violence to the demands of a particular situation, and such inflexibility could lead to even worse consequences. To be able to make the right decision, Aristotle argues, requires phronesis . He compare it to a perception, though here we are talking about an ethical perception, rather than a sensible one.