Everybody lies
Ender does not trust anyone, and one of the manifestations of that distrust is the suggestion that everyone lies, especially the adults (and in particular teachers) towards the children. For instance, Graff lies to Ender multiple times, the most obvious time being when he and Mazer pretend that the battles Ender is fighting against the buggers are actually just Mazer's battle scenarios. Ender ended up destroying almost all the buggers while thinking that he was just winning games. Even the young Valentine is insincere insofar as she writes under the pseudonym Demosthenes
Sometimes, lies are more dependable than the truth
This idea is submitted by Ender very early in the novel, when the nurse tells him that taking his monitor out will not be painful. Ender points out that since adults only say such a thing when it is going to hurt, children can always depend on the lie to warn them of the pain. In this way, the idea that everybody lies almost becomes a good thing, since it means that they are easier to figure out. A lie reveals a truth about a person's motivations.
You can't trust anybody
Ender is brought up not to trust anyone, and he often feels betrayed. For instance, Ender trusts Valentine implicitly, but she becomes the tool of the International Fleet in order to get him to continue with his training. Also, Ender realizes that he cannot always trust his friends, such as Petra--when he becomes commander and Dragon Army destroys her army, she is furious with him for months, being not much better than the other jealous commanders. Ender is not given many opportunities for friendship or trust so that he becomes fiercely independent and thus, it seems, a better commander.
Individual initiative versus central planning
Ender is chosen to be the commander who leads the fleet to victory, thereby saving the world. The principle here is that a single mind can direct the war effort better than a number of individual commanders. The military leaders have decided to follow this principle as they have sought the one most promising child to become the supreme commander. But Ender does not really want to be such a savior, and he prefers to have squadron leaders who can think and act independently with just a few organizing principles to follow. In fact, Ender's decentralized approach proves superior to that of the buggers, which is centralized in that a queen commander makes all the decisions while the workers simply follow orders.
Identity conflict
Ender Wiggin's personality is a combination of his brother's ruthlessness and his sister's compassion, which are constantly fighting each other for control. Likewise, Valentine and Peter share, to some degree, each other's characteristics, and all three siblings struggle to realize an integrated identity. In Ender's case, he chooses to win thoroughly against his enemies, but his compassion for them makes him hate himself for hurting them. Graff also struggles with his isolation of Ender for military purposes despite his real affection for Ender, wanting to be compassionate and practical at the same time.
Individual needs versus the common good
Colonel Graff's sense of duty to the human race leads him to reason with Ender, on multiple occasions, that Ender should see himself as a "tool" for the human race. He notes that "Human beings are free except when humanity needs them." Graff argues that humans become tools whenever the species needs them. Card seems to support this point of view in that we may feel sorry for Ender, but we can hardly imagine another way that the war could have been won. The happiness of one boy, it seems, should be forfeited for the sake of the race. Ender understands this point, so he makes a free choice to suffer for the sake of humanity. One thinks here of Plato's philosopher-kings in the Republic who would prefer not to rule society but who do so anyway, leading less satisfying lives in order to make the society function well enough for others to live more satisfying lives.
Friends and enemies
At every level the novel rests on antagonism: everyone is a friend or an enemy or both. The buggers and humans are enemies. Among humans, the world alliance is undermined by antagonism between, basically, the Americans and the second Warsaw Pact. The Warsaw alliance is undermined by antagonism between Muslim and non-Muslim allies. In Ender's experience, nobody can be fully trusted, but everyone is basically a friend or an enemy. This does not mean that e is always right in his identifications. He believes that Graff and Mazer are his enemies, mainly because they tell him so, but in reality they both care about him very much. For a while, after Ender becomes a commander, he cannot be sure whether Dink and Petra are still his friends, but they definitely are. In contrast, Ender thinks throughout the novel that the buggers are his enemy, but by the end of the novel, they have become his friends.
Isolation yields individual strength
Throughout the novel, Graff and Mazer isolate Ender from all of the other students at Battle School and Command School. Graff explains his reasoning multiple times; in his isolation, Ender will grow strong enough to beat the buggers. Graff thinks that Ender cannot expect anyone to help him at any time, or else he will not develop the willpower and strength to win at critcal points. Thus, Graff believes that the isolation teaches Ender to be strong. Ender reflects this idea in his treatment of Bean when Dragon Army is first created. Also, while Graff, Mazer, and Ender all hate the fact that they have to isolate their protégés, they continue on the path of isolation in order to develop them.
