An Essay in Aid of a Grammar of Assent (commonly abbreviated to the last three words) is John Henry Newman's seminal book on the philosophy of faith. Completed in 1870, the book took Newman 20 years to write, he confided to friends. Newman's aim was to show that the scientific standards for evidence and assent are too narrow and inapplicable in concrete life. He argued that logic and its conclusions are not transferable to real life decision making as such. As a result, it is inappropriate to judge the validity of assent in concrete faith by conventional logical standards because paper logic is unequal to the task. "Logic is loose at both ends," he said, meaning that the process of logic initially depends on restrictive assumptions and is thus unable to fit its conclusions neatly into real world situations. Source: Wikipedia (en)