One important concept in TCS is that of common preferences. Common preferences are policies that all parties after a successfully resolved disagreement prefer to their initial positions: everyone gets what they want. These are created through a combination of changing one's wishes to more moral ones, and creatively working out how best to proceed for everyone. TCS distinguishes between common preferences and all other possible ways of coping with prima facie disagreement, such as compromises (in which no one gets what he wants) or choosing winners and losers according to some mechanical formula like voting, taking turns, obedience to one's superior in a hierarchy and so on.
Another key concept is that of coercion. Coercion means (roughly speaking) doing things to people, or making them do things, against their will. Where common preferences are found, there is no coercion. A major difference between TCS and other educational philosophies is the idea that it is possible and desirable to raise children without intentionally coercing them.
Is non-coercion not, in itself, a mechanical rule? To think of it as such would be a misconception of TCS; moreover, such a rule could not be followed. By “it is possible” we are not implying that there is a mechanical method of achieving the lifestyle we advocate. We have something quite different in mind: like an engineer who says that starships are possible, we mean that whatever difficulties and obstacles there may be are not inherent in the situation of being an adult looking after a child, but are caused purely by not yet knowing how to solve the relevant problems. But this, in itself, is liberating because it denies the melancholy certainties of “for you own good” and “may as well get used to it” that have been self-fulfilling prophesies throughout history. What we mean is that aspiring to a non-coercive lifestyle is not like trying to build a spaceship that could exceed the speed of light: that would be an example of something that might be be desirable, but is impossible.
By “desirable”, we mean something more than that being coerced hurts and that it is not nice to be in a position of hurting people. For that leaves open the possibility of a tradeoff between that and some other even more undesirable thing. Like a political theorist who says that the transition from absolute monarchy to liberal democracy is desirable, we mean that such tradeoffs can be eliminated – again, not by a mechanical formula nor merely by wanting to, but by creatively solving the specific problems that arise.
Another possible misinterpretation of TCS is the idea that coercion is always wrong – that if one child is attacking another with a cricket bat, it is wrong to intervene. On the contrary, it is vital to protect the victim, and that might well involve stopping the attacking child against his or her will, i.e., coercively. That there would have been a way to avoid this in the first place is, at such a moment, irrelevant for all practical purposes. But in the bigger picture, it is reassuring: if the good things in life could be obtained by mechanically following a rule, then only a wicked and unworthy parent would ever fail to find a common preference with their beloved child. But TCS is not a rule. When we say that it is possible and desirable to raise children without intentionally coercing them, we don't mean that if everything goes wrong sometimes, you must be an evil shit unworthy of life, what we mean is: hey, there's hope – things need not be like this for ever!