Joseph Priestley was a renowned English theologian, author, chemist and political theorist of the 18th century. He is also regarded by many as the one who discovered oxygen. Being a scientist, he is also known for his attempts to fuse Enlightenment rationalism with Christian theism. His works contributed a lot to advancing liberal political and religious ideas. Not only he promoted free and open discussion of all kinds of ideas, he also stood for equal rights of non-believers and dissenters. His ideas led to the founding of the theological movement Unitarianism, which is known for its rejection of the concept of the Trinity, as well several other Western doctrines, like the concept of original sin, and Biblical inerrancy. Priestley also made contributions to pedagogy, the discipline dealing with the theory and practice of education. His contribution to science was so immense that he had been made a member of nearly every major scientific society by the time he passed away. Having published more than 150 works on several topics including political philosophy, science, education, and theology, he became an inspiration for many philosophers, poets and scientists, both during his lifetime, and after his death.