Locke now addresses the education of the mind. In forming a sound mind, Locke explains, we are chiefly aiming to form a virtuous mind. The most important aim of education, in other words, is to instill virtue; education is first and foremost moral education. Though academic learning is necessary and important as well, it is the child's moral character that is of the utmost concern. The strength of body, as we just saw, lay in the ability to endure hardships. The strength of mind, as it turns out, is not all that different. A strong mind (that is, a virtuous character) is one that has the ability to go without what it wants. Self-denial, according to Locke, is the principle of virtue.
A man is virtuous only insofar as he can act against his own immediate desires when reason tells him that this would be for the best. For example, imagine that a man wants to eat an entire birthday cake. Reason tells him that this would not be fair, because everyone would like a slice. A man with the principle of virtue will have the ability to listen to reason and exercise restraint over his appetites. A man without this capacity, on the other hand, will be unable to heed reason, and will eat the whole thing. The first man will behave virtuously, the second will not.
Since the key to being virtuous is to have this capacity of self-denial, the most important goal in education is to instill this capacity. Unfortunately, Locke thinks that the way that people generally raise their children has the exact opposite effect: it prevents this quality from taking hold. This is because parents tend to find their small children so adorable and lovable that they indulge their every wish. Parents find themselves unable to deny their babies anything.
The reason that overindulgence is so bad is that the mind is most malleable during extreme youth. This is precisely the time, in other words, to ensure that the child becomes pliant and obedient to reason. The first thing a child should learn is that he cannot have everything that he wants; he can only have what he wants if reason concurs that this would be for the best. Of course, children do not have much of reason their own at this age, and so they must be made obedient to their parents' reason instead. If a child becomes accustomed to denying his desires whenever his parents forbid him from indulging those desires, then, as the child matures and his own discernment develops, he will also be able to deny his desires when his own reason dictates against indulging those desires. If, on the other hand, a child is accustomed to getting whatever he wants, then he will continue to expect to get his every wish fulfilled as he matures. In other words, he will lack the principle of virtue.
In sum, a child must be made completely obedient to his parents from the earliest possible age. The child must be perfectly compliant with will of the parent because the will of parent is a surrogate for the child's future faculty of reason.
By indulging their children's desires, parents are being passively negligent concerning moral education. However, Locke accuses, parents are also often guilty of being actively negligent by teaching vices outright. Parents teach violence, revenge, and cruelty by joking about these matters. They teach vanity by fussing excessively over their children's clothes. They teach lying and equivocations by indulging in this behavior in front of their children. And they teach intemperance by constantly pressing food and drinks on their children.