Joseph Priestley was a man of the Enlightenment, a champion of reason, a foe of superstition. He was also deeply religious, and divided his life between scientific investigations and religion. In science, he is best known as the discoverer of oxygen, and for his stubborn belief in phlogiston, a now-discredited hypothetical substance supposedly mixed with all combustible matter that was released as flame in burning.
In religion, Priestley was a Dissenter, a Unitarian who took issue with the doctrines of the established Church of England. As a Dissenter, he was precluded from attending either Oxford or Cambridge universities, which at that time required for graduation assent to the Thirty-nine Articles of the Established Church, a catalog of official orthodoxy.
As Robert Schofield notes in his biography of Priestley, it was just as well that Priestley could not attend the ancient universities. Intellectual life at those institutions was hobbled by curricular requirements imposed by the Church of England. Mired in religious and political orthodoxy, Oxford and Cambridge had become pretty much irrelevant to the explosion of rational knowledge we call the Enlightenment.
Most of the important science, philosophy, history and literature of late-18th-century England was accomplished by people who had no connection to the traditional universities. Priestley took his education at a Dissenting academy, and soon found colleagues who shared his own scientific interests and liberal political and religious views, including Benjamin Franklin and Thomas Jefferson. He was a friend of American democracy, and ended his days in Pennsylvania.