to buy, or because he is blocked from access to goods and services. Included in the value of labour power is both a physical component (the minimum physical requirements for a healthy worker) and a moral-historical component (the satisfaction of needs beyond the physical minimum which have become an established part of the lifestyle of the average worker). The value of labour power is thus a historical norm, which is the outcome of a combination of factors: productivity; the supply and demand for labour; the assertion of human needs; the costs of acquiring skills; state laws stipulating minimum or maximum wages, the balance of power between social classes, etc. Buying labour power usually becomes a commercially interesting proposition only if it can yield more value than it costs to buy, i.e. employing it yields a net positive return on capital invested. However, in Marx's theory, the value-creating function of labour power is not its only function; it also importantly conserves and transfers capital value. If labour is withdrawn from the workplace for any reason, typically the value of capital assets deteriorates; it takes a continual stream of work effort to maintain and preserve their value. When materials are used to make new products, part of the value of materials is also transferred to the new products. Consequently, labour power may be hired not "because it creates more value than it costs to buy", but simply because it conserves the value of a capital asset which, if this labour did not occur, would decline in value by an even greater amount than the labour cost involved in maintaining its value; or because it is a necessary expense which transfers the value of a capital asset from one owner to another. Marx regards such labour as "unproductive" in the sense that it creates no new net addition to total capital value, but it may be essential and indispensable labour, because without it a capital value would reduce or disappear. The larger the stock of assets which is neither an input nor an output to real production, and the wealthier society's elite becomes, the more labour is devoted only to maintaining the mass of capital assets rather than increasing its value. Wages Marx regards money-wages and salaries as the price of labour power (though workers can also be paid "in kind"), normally related to hours worked or output produced. That price may contingently