 But even though a theory of labor-time as the basis of fair exchange is in principle distinguishable from a labor theory of economic value, the former is subject to many of the same problems as the latter. How, for instance, should the difference between skilled and unskilled labor time be accounted for in determining a fair exchange? Between easy and difficult labor? Labor is not homogenous, and this makes it ill-suited to serve as a currency of fair exchange.