Joseph Priestley’s statement in his letter to the editor of the Morning Chronicle, 7 March 1793, that: ‘I am not, nor ever was, a member of any political society whatever, nor did I ever sign any paper originating with any of them...‘ seems to be about as unequivocal as it could have been made. It is true that these words were written in reply to Burke’s charge that Priestley had given ‘his name to the sentiments in the Correspondence of the Revolution Society in England with the Jacobin Societies in France’, but the charge was not new, and the danger to Priestley less critical than it had been at the time of the Priestley Riots in July 1791. In the absence of any evidence to the contrary, Priestley’s denial has been taken at its face-value, and even those who have had no sympathy with his point of view have been able to regard him as honest if misguided. Two letters recently discovered, however, shed new light on Priestley’s statement and suggest that he was less frank. The first, dated 27 June 1791, just over a fortnight before the riots, is from Priestley to James Watt, inviting him ‘as a friend of liberty civil and ecclesiastical’ to join the Warwickshire Constitutional Society.1 The second is a joint reply from Matthew Boulton and James Watt to Priestley’s invitation. This suggests that Boulton must have received a similar letter from Priestley to that sent to Watt.