A human being is an “agent” in the sense of a person able to act in the world. The words “agent”, “act” and “agency” all come from the Latin “agere”, “to set in motion, drive, lead, conduct etc.” Human agents have goals in life and pursue them through their purposeful actions.
Now, if a human being is an agent or has agency, then we should give her rights because we have to define the range of activities that she is allowed to engage in. We have to decide what she can do without obstruction and defend her against obstruction if necessary. Otherwise her agency will be largely ineffective. It’s constitutive of human beings to pursue goals and hence we owe it to them to create a framework in which they can reliably do so. Whether or not they actually realize their goals is another matter, dependent upon lots of things – circumstances, luck, resources, ambition etc. We can’t and shouldn’t promise people that they’ll get what they’re after, but making it impossible for them to try is a denial of their humanity. The point is that we can only make it possible for them to try if we give them rights. Of course, people without rights or people suffering rights violations can sometimes act purposefully. But they’ll always be precarious agents. A predictable and reliable form of agency depends on respect for rights.
This kind of justification of human rights is by definition a limited one. It isn’t complete. There are people who have no agency in the relevant sense of the word – for example babies or the severely handicapped – but who still have rights. So we’ll have to look for additional justifications, which is what I’ve tried to do in the other posts in this series.