In Ethics: The Big Questions, an anthology of essays on moral issues, James P. Sterba argues that there is no meaningful difference between negative liberty and positive liberty.
Depending on who is doing the defining, negative liberty is a freedom from interference or obligation. Positive liberty is liberty which is obtained at the expense of others, usually without their consent.
In an entertaining attempt at Newspeak, Sterba attempts to frame socialist wealth redistribution as a negative liberty.
What is at stake is the liberty of the poor not to be interfered with in taking from the surplus possessions of the rich what is necessary to satisfy their basic needs. Needless to say, libertarians would want to deny that the poor have this liberty. But how could they justify such a denial? As this liberty of the poor has been specified, it is not a positive right to receive something, but a negative right of non-interference.
If we forced a productive member of society to go to work, telling him that over half his wages were going to a welfare recipient, we would all agree that the welfare recipient is a beneficiary of positive liberty. But what if we did not tell the productive worker that we were going to take his wages, and after he returned home from a hard day at work, we simply requested that he not interfere with any welfare recipients who drop by and happen to empty his wallet – would this be any different?
Whether the obligation we place on the productive worker happens after the earning, or before the earning, the liberty provided to the welfare recipient was still at the expense of the worker. That would make it a positive liberty.





Tibor Machan, libertarian philosopher associated with the Mises Institute wrote this on the topic:
http://www.thefreemanonline.org/featured/the-perils-of-positive-rights/
Isaiah Berlin’s Two Concepts of Liberty is the definitive essay on negative v positive liberty, although I think he was a bit too accommodating of positive liberty, even as he warned of the danger of the positive liberty to individual freedom.