 Locke’s argument is not without difficulties. Jeremy Waldron (1983) argued that the idea of mixing one’s labor is incoherent—actions cannot be mixed with objects. P. J. Proudhon (1840) argued that if labor was important, the second labor on an object should ground a property right in an object as reliably as the first labor. Nozick (1974) asked why labor mixing generated property rights rather than a loss of labor. Waldron (1983) and Perry (1978) have argued that mixing one’s labor with an unowned object should yield more limited rights than rights of full ownership. Finally, if the skills, tools, and inventions used in laboring are social products, then perhaps individual claims to title have been undermined (Grant 1987; Hettinger 1989).