In October 1767, he received from the presbytery of Paisley his preacher's license, not, however, without some opposition on the ground of want of orthodoxy in the doctrines of the Church of Scotland.
[2] For some years he was usefully employed in compiling a complete catalogue of the books, arranged in two parts, one under an alphabet of authors, and the other according to the position of the volumes on the shelves.
Arthur was appointed assistant professor in moral philosophy through the influence of Dr. Thomas Reid, who was obliged to give up his full professorial duties on account of increasing years.
They devoted part of it to the publication of his posthumous "Discourses on Theological and Literary Subjects",[3] which were edited, with a memoir by his friend William Richardson.
A. F. Tytler, in a note upon a letter of Dr. Reid, remarks: "Mr. Arthur, a man of learning, abilities, and worth, filled the chair of moral philosophy … with a reputation which did not disappoint the hopes of his respectable predecessor".