Negative liberty is the absence of obstacles, barriers or constraints. One has negative liberty to the extent that actions are available to one in this negative sense. Positive liberty is the possibility of acting — or the fact of acting — in such a way as to take control of one’s life and realize one’s fundamental purposes. While negative liberty is usually attributed to individual agents, positive liberty is sometimes attributed to collectives, or to individuals considered primarily as members of given collectives.
The idea of distinguishing between a negative and a positive sense of the term “liberty” goes back at least to Kant, and was examined and defended in depth by Isaiah Berlin in the 1950s and ’60s. Discussions about positive and negative liberty normally take place within the context of political and social philosophy.
Two Concepts of Liberty
Imagine you are driving a car through town, and you come to a fork in the road. You turn left, but no one was forcing you to go one way or the other. Next you come to a crossroads. You turn right, but no one was preventing you from going left or straight on. There is no traffic to speak of and there are no diversions or police roadblocks. So you seem, as a driver, to be completely free. But this picture of your situation might change quite dramatically if we consider that the reason you went left and then right is that you’re addicted to cigarettes and you’re desperate to get to the tobacconists before it closes. Rather than driving, you feel you are being driven, as your urge to smoke leads you uncontrollably to turn the wheel first to the left and then to the right. Moreover, you’re perfectly aware that your turning right at the crossroads means you’ll probably miss a train that was to take you to an appointment you care about very much. You long to be free of this irrational desire that is not only threatening your longevity but is also stopping you right now from doing what you think you ought to be doing. 
This story gives us two contrasting ways to think about liberty. If we consider the absence of obstacles external to the agent, the agent is free. On the other hand if we consider freedom as the presence of control on the part of the agent, the agent is not free, or self-determined. His actions are determined by an irrational passion that he would wish to be rid of. In this sense, while the first view of liberty is simply about how many doors are open to the agent, the second view it is more about going through the right doors for the right reasons.
An initial way of distinguishing the two forms of freedom is the focus on external (negative liberty) versus internal (positive liberty) constraints. In its political form, positive freedom has often been thought of as necessarily achieved through collectivity. In Rousseau’s theory, all citizens voluntarily alienate part of their natural liberty in order to give foundation to civil liberty, the State, and the General Will. Civil liberty is taken to provide an advantage over the state of nature, and rights often come paired with duties. “[I]t is in order that we may not fall victims to an assassin that we consent to die if we ourselves turn assassins.” — Jean Jacques Rousseau, The Social Contract, Book 2, Chapter 5, “The Right of Life and Death”
Positive liberty projects can often lead to tyranny; however, the foundation of the State and citizenship lies in an act of positive liberty, the purest (fundamental) form of negative liberty being the state of nature.
One Concept of Liberty: Freedom as a Triadic Relation
There are many ways to compare and contrast these different notions of liberty. In order to clarify things, Gerald MacCallum put forward a theoretical framework to understand both these concepts and their variations :
MacCallum defines the basic concept of freedom — the concept on which everyone agrees — as follows: a subject, or agent, is free from certain constraints, or preventing conditions, to do or become certain things. Freedom is therefore a triadic relation, that is, a relation between three things:
1) an agent,
2) certain preventing conditions,
3) and certain doings or becomings of the agent.
Any claim about the presence or absence of freedom in a given situation will therefore make certain assumptions about what counts as an agent, what counts as a constraint or limitation on freedom, and what counts as a purpose that the agent can be described as either free or unfree to carry out.
To illustrate MacCallum’s point, let us return to the example of the smoker driving to the tobacconists. In describing this person as either free or unfree, we shall be making assumptions about each of MacCallum’s three variables. If we say that the driver is free, what we shall probably mean is that an agent, consisting in the driver’s empirical self, is free from external (physical or legal) obstacles to do whatever he or she might want to do. If, on the other hand, we say that the driver is unfree, what we shall probably mean is that an agent, consisting in a higher or rational self, is made unfree by internal, psychological constraints to carry out some rational, authentic or virtuous plan. Notice that in both claims there is a negative element and a positive element: each claim about freedom assumes both that freedom is freedom from something (i.e., preventing conditions) and that it is freedom to do or become something. The dichotomy between “freedom from” and “freedom to” is therefore a false one, and it is misleading say that those who see the driver as free employ a negative concept and those who see the driver as unfree employ a positive one. What these two camps differ over is the way in which one should interpret each of the three variables in the triadic freedom-relation. More precisely, we can see that what they differ over is the extension to be assigned to each of the variables.
Those commonly identified with negative liberty tend to define the agent as the purely empirical present self. Most define the preventing conditions or obstacles to liberty as explicit intervention from other agents. This mostly is an oversimplification, as intervention may be helpful or harmful. What matters to a person is achieving a goal; therefore freedom from intervention can be relevant only if that intervention was hindering freedom to achieve the goal, otherwise it may even be hurtful (consider public education for example). They leave the doings or becomings of the agent mostly undefined, and as open as possible.
In this sense the poor in a capitalist society can be considered as free as the rich, as they are mostly free from intervention, and indeed a vast majority of them internalize a notion of freedom that makes their current situation justifiable, even though they lack the possibilities of the rich.
“Aristotle was right; but he took the effect for the cause. Nothing can be more certain than that every man born in slavery is born for slavery. Slaves lose everything in their chains, even the desire of escaping from them: they love their servitude, as the comrades of Ulysses loved their brutish condition. If then there are slaves by nature, it is because there have been slaves against nature.” — Jean Jacques Rousseau, The Social Contract, Book 1, Chapter 2, “The First Societies”
Those identified with positive liberty tend to define the agent as simultaneously more and less extensive than those do who are in the negative camp : they think of the agent as having a greater extension than in ordinary discourse in cases where they identify the agent’s true desires and aims with those of some collectivity of which she is a member; and they think of the agent as having a lesser extension than in ordinary discourse in cases where they identify the true agent with only a subset of her empirical beliefs and desires — i.e., with those that are rational, authentic or virtuous. The set of preventing conditions tends also to be more extensive, whether caused by direct or indirect means, relating to internal or external factors. The set of doings or becomings of the agent is more specifically defined, whether through forms of personal or social ideals. They tend to restrict the relevant set of actions or states to those that are rational, authentic or virtuous, whereas those in the negative camp tend to extend this variable so as to cover any action or state the agent might desire.
A criticism of MacCallum’s framework is that it captures possibilities, potentialities, freedom only as an opportunity concept. Freedom, if it consists of self-direction and self-mastery, must imply actually doing certain things in certain ways, as opposed to mere possibility, such that freedom as an exercise concept. This criticism is not necessarily valid. Most of the theorists that are traditionally located in the positive camp do not distinguish between freedom as the absence of constraints and freedom as the doing or becoming of certain things. If x is self-actualizing, and nothing prevents me from doing x (whether internal or external conditions), then I will do x. The absence of all factors that could prevent the action x is, quite simply, equivalent to the realization of x.
Meritocracy will provide a society of equal opportunity where society’s best would be put in charge of their areas of expertise. In today’s world the basic “unit” can be said to be the family. Privileged families pass on advantages (i.e., wealth) to their children, often to the great detriment of everyone else. Meritocracy puts community above family, for the benefit of both. It’s fundamentally a project of positive liberty. A fitting motto would be All for one and one for all.
[http://plato.stanford.edu/entries/liberty-positive-negative Positive and Negative Liberty] entry by Ian Carter in the [http://en.wikipedia.org/wiki/Stanford_Encyclopedia_of_Philosophy Stanford Encyclopedia of Philosophy]