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Free love

Shelley's advocacy of free love drew heavily on the work of Mary Wollstonecraft and the early work of William Godwin. In his notes to Queen Mab, he wrote: "A system could not well have been devised more studiously hostile to human happiness than marriage." He argued that the children of unhappy marriages "are nursed in a systematic school of ill-humour, violence and falsehood". He believed that the ideal of chastity outside marriage was "a monkish and evangelical superstition" which led to the hypocrisy of prostitution and promiscuity.

Shelley believed that "sexual connection" should be free among those who loved each other and last only as long as their mutual love. Love should also be free and not subject to obedience, jealousy and fear. He denied that free love would lead to promiscuity and the disruption of stable human relationships, arguing that relationships based on love would generally be of long duration and marked by generosity and self-devotion.

When Shelley's friend T. J. Hogg made an unwanted sexual advance to Shelley's first wife Harriet, Shelley forgave him of his "horrible error" and assured him that he was not jealous. It is very likely that Shelley encouraged Hogg and Shelley's second wife Mary to have a sexual relationship.