John Stuart Mill was an "intellectual," though not a professional intellectual in the sense of earning his living by his pen and thoughts. As such he lived mainly by ideas, and it is his ideas that cause most of us to be interested in him. If all we had was the record of his emotional struggles, his mental crisis, we would think it an interesting human story, but of no real consequence for history. Only in the light of John Stuart Mill's importance as a thinker does his emotional life take on a significant historical interest. Mill perceived his own mental development as occurring in three definite stages. The first stretches to about 1830–1831, what he calls "the old Westminster Review period." The second period terminates in around 1844, with the success of the Logic, which led to publication the next year of the political economy essays.