 Within this revised work he also made the radical proposal that the whole wage system be abolished in favour of a co-operative wage system.Nonetheless, some of his views on the idea of flat taxation remained, albeit altered in the third edition of the "Principles of Political Economy" to reflect a concern for differentiating restrictions on "unearned" incomes, which he favoured, and those on "earned" incomes, which he did not favour.Mill's "Principles", first published in 1848, was one of the most widely read of all books on economics in the period.