text: But why is the Good non-existent in a tree or in a dumb beast? Because there is no reason there, either. For the same cause, then, the Good is non-existent in a child, for the child also has no reason; the child will reach the Good only when he reaches reason. There are animals without reason, there are animals not yet endowed with reason, and there are animals who possess reason, but only incompletely; in none of these does the Good exist, for it is reason that brings the Good in its company. What, then, is the distinction between the classes which I have mentioned? In that which does not possess reason, the Good will never exist. In that which is not yet endowed with reason, the Good cannot be existent at the time. And in that which possesses reason but only incompletely, the Good is capable of existing, but does not yet exist. This is what I mean, Lucilius: the Good cannot be discovered in any random person, or at any random age; and it is as far removed from infancy as last is from first, or as that which is complete from that which has just sprung into being. Therefore, it cannot exist in the delicate body, when the little frame has only just begun to knit together. Of course not – no more than in the seed. Granting
  the truth of this, we understand that there is a certain kind of Good of a tree or in a plant; but this is not true of its first growth, when the plant has just begun to spring forth out of the ground. There is a certain Good of wheat: it is not yet existent, however, in the swelling stalk, nor when the soft ear is pushing itself out of the husk, but only when summer days and its appointed maturity have ripened the wheat. Just as Nature in general does not produce her Good until she is brought to perfection, even so man's Good does not exist in man until both reason and man are perfected. And what is this Good? I shall tell you: it is a free mind, an upright mind, subjecting other things to itself and itself to nothing. So far is infancy from admitting this Good that boyhood has no hope of it, and even young manhood cherishes the hope without justification; even our old age is very fortunate if it has reached this Good after long and concentrated study. If this, then, is the Good, the good is a matter of the understanding.