In 1787, he published his essay on the _Theory of Moods and Verbs_, and in 1792, _Philosophical_ and _Literary Essays_. He was a great student of words, loved epigram, and spent much of his leisure in translating poetry. He was also interested in metaphysics, but as his great maxim was that in metaphysics there could be no discovery, his writings on this subject do not appear to have added much to his fame. Throughout these years, too, he kept up a constant correspondence with his cousin Thomas Reid, and proved himself just the appreciative critic that Reid required in the writing of his books. Dugald Stewart and Gregory together revised the proofs of Reid’s _Essays on the Intellectual Powers_, and to them this book was dedicated. ‘I send you,’ writes Reid, ‘what I propose as the title of my Essays, with an epistle which I hope you and Mr Stewart will allow me to prefix to them. Whether your name should go first on account of your doctor’s degree, or Mr Stewart’s, I leave you to adjust between yourselves. I know not how to express my obligations to you both for the aid you have given me.’ Towards the end of 1790 it became apparent that Cullen, the greatest doctor of his time was failing in strength, and on his resigning the Chair of the Practice of Physic the Town Council reappointed him in kindly recognition of his great services to the university, but appointed James Gregory to be joint-professor during his lifetime with the sole right of survivorship. This comradeship did not last long, for in the same year Cullen died. To no less strong man could the task of succeeding this veteran teacher, who had raised the reputation of the Edinburgh School to such a height, have been wisely entrusted.