Identification and desert
Logically void, uncompelling morally, and of indeterminate application to boot, the notion of labour-mixing can evoke blank scepticism. Some express themselves quite unmoved by it.41 And yet, others continue not merely to affirm it, but to affirm it as embodying an intuition whose power is, to them, manifest. One is bound to surmise that the affirmation draws strength from elsewhere. Earlier, I suggested with regard to Locke that the labour-mixing principle might ride on other things, related to but distinct from it. I now argue that that is so. Two other ideas are in play: one, (loosely) personal extension; the other, desert.
As to the first, I am not myself persuaded it is of much significance in Locke. But one commentator proposes so. Discounting that Locke's metaphor could be intended literally, he proffers instead a psychological meaning. The idea is of 'an extension of the personality to physical objects', so that they become 'part of our very selves'. We have a 'feeling of unification' with them. Through labour, 'something of the spiritual ego [is] infused into the object'; and for others than the labourer then to have a right to the object would imply 'a right over another free individual, which is out of the question.'42 However it may be with Locke, this idea of something of the person (here their 'spiritual ego') in the thing, so the latter becomes part or extension of the former, certainly figures in other advocacy from labour-mixing to exclusive property rights. We are told by Murray Rothbard, for example, that Crusoe, in mixing his labour with the soil, is 'stamping the imprint of his personality and his energy on the land'; and that a man has 'the right to own the product that he has made, by his energy and effort, into a veritable extension of his own personality'; and (quoting earlier advocacy) that the product is 'an emanation from his being' - he 'has left a fragment of his own person in the thing.'43
I consider three possibilities suggested by these locutions. First, what there is of the person in the thing is an ineffable substance, not open to observation or discovery. The argument then rests on an arcane metaphysic and need not detain us. Second, what there is of the person in the thing is just the person's labour. Labour, however, is not a substance in the thing; it is an activity. Third, the meaning is entirely pyschological. There is nothing of the person actually in the thing, but the person feels a powerful identification with it and would experience its loss as a wound; perhaps more grievously still. There is no question that working long or hard on something can produce this type of identification. Our earlier example of the sculptor partly traded on its likelihood; and in general those who have done practically any sort of work will be familiar with it.
But the feeling is also produced in other ways. Mere long possession can do it. (He writes each day at this bureau; periodically rearranges its contents. She has lived here so long.) Even wanting something badly enough can do it. Used in support of exclusively labour-based appropriative rights, this type of identification is illicitly exploited, for it is not special to labour. Further, if it carries moral weight, it must do so as a species of need, and has to be assessed, then, relative to other needs. Again, should one respond that need due to an identification formed through labour counts in a way that other kinds of identification or of need do not, the result will be that 'extension of the personality' is not, after all, the reason for labour-based property entitlements - labour is.
 See Thomas Nagel, 'Libertarianism Without Foundations', in Paul, p. 195; Honoré, 'Property, Title and Redistribution', pp. 107-8; and O'Neill, p. 314. Also relevant here are the telling remarks on formal principles of justice in acquisition (PJAs) by Waldron: pp. 265, 267-8, 270-1.
 Karl Olivecrona, 'Locke's Theory of Appropriation', Philosophical Quarterly, 24 (1974), pp. 224-6. Cf. Becker pp. 48-9, for the suggestion of a psychological dimension to the labour theory of acquisition.
 The Ethics of Liberty, pp. 33, 48, 67 n. 2; cf. his 'Justice and Property Rights', p. 109.
(Part 10 is here.)