An improvement in organisation or in foresight which diminishes 'frictional' unemployment; (b) a decrease in the marginal disutility of labour, as expressed by the real wage for which additional labour is available, so as to diminish 'voluntary' unemployment; (c) an increase in the marginal physical productivity of labour in the wage goods industries (to use Professor Pigou's convenient term for goods upon the price of which the utility of the money wage depends); or (d) an increase in the price of non wage goods compared with the price of wage goods, associated with a shift in the expenditure of non wage earners from wage goods to non wage goods.