Every agent acts for what it thinks is a good, even if it misses the mark.
1 Next after this we must show that every agent acts for a good.
2 That every agent acts for an end has been made clear from the fact that every agent tends toward something definite. Now, that toward which an agent tends in a definite way must be appropriate to it, because the agent would not be inclined to it except by virtue of some agreement with it. But, what is appropriate to something is good for it. So, every agent acts for a good.
Notes Be careful: a good is not necessarily the Good.
3 Again, the end is that in which the appetitive inclination of an agent or mover, and of the thing moved, finds its rest. Now, the essential meaning of the good is that it provides a terminus for appetite, since “the good is that which all desire.” Therefore, every action and motion are for the sake of a good.
4 Besides, every action and movement are seen to be ordered in some way toward being, either that it may be preserved in the species or in the individual, or that it may be newly acquired. Now, the very fact of being is a good, and so all things desire to be. Therefore, every action and movement are for the sake of a good.
5 Moreover, every action and movement are for the sake of some perfection. Even if the action itself be the end, it is clear that it is a secondary perfection of the agent. But, if the action be a changing of external matter, it is obvious that the mover intends to bring about some perfection in the thing that is moved. Even the thing that is moved also tends toward this, if it be a case of natural movement. Now, we call what is perfect a good. So, every action and movement are for the sake of a good.
6 Furthermore, every agent acts in so far as it is in act, and in acting it tends to produce something like itself. So, it tends toward some act. But every act has something of good in its essential character, for there is no evil thing that is not in a condition of potency falling short of its act. Therefore, every action is for the sake of a good.
7 Again, an intelligent agent acts for the sake of an end, in the sense that it determines the end for itself. On the other hand, an agent that acts from a natural impulse, though acting for an end, as we showed in the preceding chapter, does not determine the end for itself, since it does not know the meaning of an end, but, rather, is moved toward an end determined for it by another being.
Now, the intelligent agent does not determine the end for itself, unless it do so by considering the rational character of the good, for an object of the intellect is only motivating by virtue of the rational meaning of the good, which is the object of the will. Therefore, even the natural agent is neither moved, nor does it move, for the sake of an end, except in so far as the end is a good; for the end is determined for the natural agent by some appetite. Therefore, every agent acts for the sake of a good.
Notes In that first paragraph is the (correct) notion of design. Even suicide is seen as a good at the moment, for instance to remove or relieve mental torment. But suicide is not Good.
8 Besides, there is the same general reason for avoiding evil that there is for seeking the good, just as there is the same general reason for moving downward and for moving upward. But all things are known to flee from evil; in fact, intelligent agents avoid a thing for this reason: they recognize it as an evil thing. Now, all natural agents resist corruption, which is an evil for each individual, to the full extent of their power. Therefore, all things act for the sake of a good.
9 Moreover, that which results from the action of an agent, but apart from the intention of the agent, is said to happen by chance or by luck. But we observe that what happens in the workings of nature is either always, or mostly, for the better.
Thus, in the plant world leaves are arranged so as to protect the fruit, and among animals the bodily organs are disposed in such a way that the animal can be protected. So, if this came about apart from the intention of the natural agent, it would be by chance or by luck. But this is impossible, for things which occur always, or for the most part, are neither chance nor fortuitous events, but only those which occur in few instances. Therefore, the natural agent tends toward what is better, and it is much more evident that the intelligent agent does so. Hence, every agent intends the good when it acts.
Notes Recall the luck and chance are not real, but pertain to your mental state, your understanding. A fruit tree will produce fruit unless it is prevented in doing so by some cause or mechanism.
10 Furthermore, everything that is moved is brought to the terminus of the movement by the mover and agent. So, the mover and the object moved must tend toward the same thing. Now, the object moved, since it is in potency, tends toward act, and so toward the perfect and the good, for it goes from potency to act through movement. Therefore, both the mover and the agent always intend the good in their movement and action.
11 This is the reason why the philosophers, in defining the good, have said: “the good is what all desire.” And Dionysius states that “all crave the good and the best [De div. nom. IV, 4].”