Take the right to free speech for instance. Negatively, it means that constraints on speech should be removed as much as possible. Legal people are used to view this and other rights in such a negative sense, because courts and judges are well-placed to remove constraints: they can invalidate or refuse to apply laws and policies that constrain rights such as speech rights; they can punish or fine people that constrain rights etc.
However, this legal interpretation of rights is insufficient. I’ve often argued that human rights are positive as well as negative, in the sense that they don’t merely require the removal of constraints but also the provision of prerequisites. Take again the right to free speech: we can’t say that anyone who does not suffer constraints on her speech has an effective right to free speech. While no one or no law may prohibit or stop a person from speaking, her poverty, lack of education etc. can make it very hard for her to speak effectively. I personally, for instance, find it much easier to blog when I’m able to read inspiring material. My freedom of speech, as I exercise it on this blog, would be non-existing if I wasn’t part of a global conversation about human rights. I would still have the negative right to speak, but I wouldn’t have anything to speak about. And the freedom to do what you like without impediments doesn’t make sense if you don’t have anything to do.
There may be a difference in degree: some rights, in most circumstances, are perhaps more positive than negative or vice versa. I guess the right to food is most often a positive right in the sense that it requires provision rather than forbearance. Although even in this example, we find that famines aren’t usually caused by the absence or non-provision of food but by constraints on the effective distribution of food.