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80 Piero Sraffaterms of labour commanded for different distributions of the nationalincome. 4Thus Ricardo prefers to measure commodities in terms of the labourdirectly or indirectly necessary for their production. This type of measurehas the desirable property of being invariant to changes in the distributionof income. Ricardo is thus able to use a single magnitude, labour,to represent wages, profits and the national income (total profits beingequal, in value terms, to the difference between the labour requiredto produce the national income and the labour required to producemeans of subsistence and means of production). The advantage of thisstandard of measure is that the rate of profits is determined as a ratioof homogeneous physical magnitudes, since both profits and capitaladvanced are expressed in terms of quantities of labour (much like the‘corn model’, where profits and capital advanced in the agriculturalsector are both expressed in terms of corn).However, the property of the labour standard that counts most forRicardo is that it expresses the value of a commodity in terms of its costto society, namely in terms of the labour that has to be exerted in orderto obtain it. Thus it constitutes an invariable standard with respect tochanges in the techniques of production (one hour of labour is onehour of labour). The effect of technical progress can be represented bythe reduction in the amount of labour directly or indirectly required forproduction, hence by the reduction in the labour value of commoditiesdirectly or indirectly affected by technical progress. It was on this basisthat the labour standard had already gained substantial support, evenbefore Ricardo’s introduction of the concept, from the exponents, suchas Locke, of the ‘natural law’ proposition which holds that propertyrights derive from the act of expending labour in productive activities. 5Ricardo seems to come very close to such a conception, especially ina passage from his last written work, the essay on ‘Absolute value andexchangeable value’; ‘I may be asked what I mean by the word value,and by what criterion I would judge whether a commodity had or hadnot changed its value. I answer, I know no other criterion of a thingbeing dear or cheap but by the sacrifices of labour made to obtain it.’ 64However, Ricardo criticises Smith’s measure not on this ground, but rather in termsof the possible confusions that could result from the use of such a measure to analysea situation where there are changes in technology. Cf. Ricardo (1817: 16–20).5See, for example, Locke (1690: 129–41) (II.5). However, Locke uses such termsas ‘labour’ and ‘property’ in a special sense, differing from common use: cf.Roncaglia (2001, § 4.2). After Ricardo, a somewhat similar position is held by theso-called Ricardian socialists.6Ricardo (1951–5, vol. 4: 397), quoted by Sraffa (1951: xlvi).The Standard Commodity 81It is now generally recognised, however, that the labour directly orindirectly required for production is not an unambiguous standard ofmeasure for the analysis of income distribution. As Garegnani (1960:19 and 7) points out, capital in particular must be measured ‘in termsof quantities: (a) independent of changes in distribution so that theycan be included among the givens which determine the rate of profits;(b) which can be expressed in terms of a known relation to the value ofcapital to be measured’. In fact, ‘in order for the results of the theory tobe of significance […] the commodities expressed in terms of the commonstandard of measure should be in the same proportions as they areexchanged in the actual situation examined’.The second condition is not satisfied by the labour standard. Whenthe rate of profits is positive, relative prices differ from the ratios ofquantities of labour required to produce the different commodities,except when the various industries have an identical proportion oflabour to (the value of ) the means of production. 7This difficulty arises for Ricardo’s analysis because he tries to use a singlestandard of value to deal with two different and distinct problems.The first problem relates to the identification of changes in relativeprices due to changes in the methods of production. The second concernschanges in relative prices caused by a change in the distribution ofincome. For the first problem a measure of ‘absolute’ value, such as thelabour required for production, is adequate. But, as Sraffa observes, 8in this attempt to extend the application of absolute value to thesecond problem (that of distinguishing the two sorts of changes inexchangeable values) Ricardo was confronted with this dilemma:whereas the former application presupposes an exact proportionalitybetween relative and absolute value, the latter implies a variabledeviation of exchangeable from absolute value for each individualcommodity. This contradiction Ricardo never completely succeededin resolving, as is apparent from his last paper.7Cf. Sraffa (1960: 13). Sraffa adds in a footnote that even if knowledge of thevalues is necessary for the calculation of this set of proportions, because it isnecessary to aggregate the various means of production in a unique magnitude,when such proportions are equal (unequal) in the various industries for a givenset of values (corresponding to a given level of wages), they are equal (unequal)for all sets of values obtainable when wages vary between zero and their maximumlevel, corresponding to a zero rate of profits.8Sraffa (1951: xlvii). On this point cf. Meldolesi (1966: 612–35).