Two great theories compete to explain what a right really is:
(a) The Will Theory
Associated with Savigny and Windscheid, and in a different form with Hegel, the will theory holds that a right is a power of the will, an authority conferred on the right-holder to act, forbear or demand. The essence of a right is individual liberty and choice: my right over my property is my sphere of free action, my "little empire." Windscheid defined a right as "a power or authority conferred on a person by law" — the famous "claim" (Anspruch) idea that influenced German civil law.
Critique: The theory explains the active rights of healthy adults badly... rather, it fails to explain the rights of those without meaningful will — infants, the insane, the comatose, and juridical persons themselves. An infant's inheritance cannot be a "power of will" because the infant has no developed will. It also cannot easily explain rights one cannot waive (inalienable fundamental rights, child support entitlements).
(b) The Interest Theory
Associated with Rudolf von Jhering (Ihering), the interest theory holds that a right is a legallyprotected interest — not an expression of will but of benefit. Jhering: rights exist not because the holder wills, but because law protects something of value to him. The infant and the lunatic have rights precisely because they have interests (in being fed, in their property), whether or not they can exercise will.
Critique: If a right is any protected interest, the theory proves too much. A shopkeeper has an interest in customers; law protects him against fraud, but he has no "right" to customers. Protection of an interest is a necessary but not sufficient condition of a right — protection must be individuated, owed to this person as their right.
(c) Reconciliations
Salmond synthesised: a legal right is an interest recognized and protected by a rule of right justice — taking the interest element from Jhering but insisting it is the recognition by law that converts interest into right. Holland offered the "capacity to control the acts of another with the assistance of the State." The most rigorous modern analysis is Hohfeld's, discussed below, which dissolves "right" into four distinct concepts (claim, liberty, power, immunity) and shows that the single word "right" confuses them all.