Although Joseph Priestley was notorious for rejecting much of orthodox Christianity and replacing it with a materialistic Unitarianism, in another respect he was an orthodox theist of his time in that he passionately upheld the Argument from Design. The Argument from Design was the heart of his “rational religion”. He contended that natural order, especially biological order, could only be successfully explained by intentional agency. At the time, however, the Argument was coming under attack, first from David Hume, then from (...) Matthew Turner, and lastly from Erasmus Darwin. Priestley replied to each of these critics. This article surveys his replies. The three critics of the Argument contended that intelligent agency could offer only a weak explanation of natural order or that natural order is self-explanatory or that natural mechanisms can explain biological order. Priestley in turn critiqued all three contentions, arguing that the Argument is a strong explanation; that natural order cannot be self-explanatory; and that the proposed natural explanations conflict with the empirical evidence. (shrink)