I answer that, If we speak of the goodness which the external action derives from the will tending to the end, then the external action adds nothing to this goodness, unless it happens that the will in itself is made better in good things, or worse in evil things. This, seemingly, may happen in three ways. First in point of number; if, for instance, a man wishes to do something with a good or an evil end in view, and does not do it then, but afterwards wills and does it, the act of his will is doubled and a double good, or a double evil is the result. Secondly, in point of extension: when, for instance, a man wishes to do something for a good or an evil end, and is hindered by some obstacle, whereas another man perseveres in the movement of the will until he accomplish it in deed; it is evident that the will of the latter is more lasting in good or evil, and in this respect, is better or worse. Thirdly, in point of intensity: for these are certain external actions, which, in so far as they are pleasurable, or painful, are such as naturally to make the will more intense or more remiss; and it is evident that the more intensely the will tends to good or evil, the better or worse it is.
On the other hand, if we speak of the goodness which the external action derives from its matter and due circumstances, thus it stands in relation to the will as its term and end. And in this way it adds to the goodness or malice of the will; because every inclination or movement is perfected by attaining its end or reaching its term. Wherefore the will is not perfect, unless it be such that, given the opportunity, it realizes the operation. But if this prove impossible, as long as the will is perfect, so as to realize the operation if it could; the lack of perfection derived from the external action, is simply involuntary. Now just as the involuntary deserves neither punishment nor reward in the accomplishment of good or evil deeds, so neither does it lessen reward or punishment, if a man through simple involuntariness fail to do good or evil.