He was the eldest son of James Mill, a Scotsman, who after moving to London became good friends with Jeremy Bentham and as part of a group the 'philosophical radicals' widely promoted and advocated utilitarianism.
In an effort to indoctrinate his son and make him a 'calculating machine,' James taught him to read Greek at the age of 3 and Latin at 8.
By his early teens, John Stuart Mill had read all the major Greek and Latin works and had an extensive overview of history.
He was also well versed in law, psychology, economics, mathematics and logic. Unfortunately, at the age of 20, perhaps from undernourishment of his emotions, the 'calculating machine' had a nervous breakdown.
He began to reflect critically on his own happiness and after being brought to tears by a book he was reading, and by renewing his interest in poetry, culture and the arts, he started to recover. Realizing that he had not lost his capacity to feel, Mill slowly found a new zest for life and a renewed enthusiasm for his work.
After his breakdown, Mill began to react against the intellectual influence of both his father and Jeremy Bentham. His brand of utilitarianism is a refinement of both of their views. Like Bentham, Mill maintained that the guide to moral action should be the maximization of pleasure and the minimization of pain.
For Mill, however, in his "Greatest Happiness Principle....actions are right in proportion as they tend to promote happiness, wrong as they tend to produce the reverse of happiness. By happiness is intended pleasure, and the absence of pain; by unhappiness, pain, and the privation of pleasure."
Mill also identified two failings in Bentham's theory. First of all, in calculating relative amounts of pain and pleasure, Bentham valued each unit of good or bad equally. He made no room for distinctions such as the pain that is experienced from the death of a pet compared to the pain one might experience in losing a close relative.
Secondly, he makes no distinction between higher and lower pleasures. Although he distinguishes between pleasures in terms of their quantity, he makes no distinction in their quality. To Bentham, all that matters is the duration and intensity of the pleasures produced.
Conversely, for Mill, cerebral pleasures such as those of thought, feeling and imagination deserve greater weight than those of body and sense. He wrote that "it is better to be a human being dissatisfied than a pig satisfied; better to be Socrates dissatisfied than a fool satisfied." For Mill, the distinction between higher and lower pleasures is absolutely necessary when taking utilitarian calculation into account.
Mill's system of utilitarianism was one of radical liberalism. He felt that people should be able to do what they like, even if it jeopardizes their own happiness, as long as they don't harm anyone else.
His core ethical philosophy is exemplified in "actions are right in proportion as they tend to promote happiness; wrong as they tend to produce the reverse of happiness" and in his famous work On Liberty he writes that "the only purpose for which power can be rightfully exercised over any member of a civilized community, against his will, is to prevent harm to others."
Towards the end of his life Mill wrote The Subjection of Women, a compelling appeal for the equality of women. In it he compares the legal status of women to the status of slaves and argues for equality in marriage and under the law.
He points out that it is because women have been subjected to male dominance for so long that they behave in certain ways, not because they are naturally predisposed to such behaviors. He declares that it is morally wrong for a man and woman to engage in a relationship in which only one of them enjoys the freedom of choice.
The overall aim of John Stuart Mill's philosophy was to contribute to the progress and understanding of human existence, well being and individual freedom.
His views are rooted in the works of the British empiricism of John Locke, George Berkeley and David Hume, as well as the utilitarianism of Jeremy Bentham. While his work, for the most part was not entirely original, he added new depth and perspective to the philosophies.
Although Mill's influence has fluctuated over the years, he is generally recognized as the most effective defender of the empiricist point of view. Likewise, his writings in ethics and liberal social and political philosophy continue to be read and taught in universities throughout.