is the 'connaturality' what makes pleasure able to be unreasoned?

what is the cause of the difference - is it something fundamental or the fact that Aquinas used only dist. betw. ext. and int.? Now, if it is only that dist., would there not be a fundamenal reason he chose to do that? "Joy" is not given to brute beasts - sorrow is, because it concerns imagination as well - imagination and intellect - which refers to understanding rather than