Illative sense

An Essay in Aid of a Grammar of Assent (commonly abbreviated to the last three words) is John Henry Newman's book on the philosophy of faith, his seminal work. While it was completed in 1870, Newman revealed to friends that it took him 20 years to write the book.

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.

The Grammar was an apologia for faith. Newman was concerned with defending faith as a legitimate product of rational human activity—that assent is not contrary to human nature. He wrote this book against the background of British Empiricism which restricted the strength and legitimacy of assent to the evidence presented for it. John Locke, David Hume and John Stuart Mill, a contemporary of Newman, were the primary Empiricists that Newman was engaged with philosophically.

The Grammar is divided into two sections. The first is entitled "Assent and Apprehension", which deals with believing what one does not understand. The second is entitled "Assent and Inference" and it addresses the issue of believing what cannot be absolutely proven.

Both parts deal with assent or belief. The first part discussed the relationship between assent and apprehension—what level of intelligent appropriation of a teaching is necessary to believe in that teaching. This section ultimately turns on a distinction between apprehension and understanding. Newman's view was that one can believe as long as one apprehends, even if one does not understand. For example, one may not understand the doctrine of the Trinity, i.e., resolve the individual propositions of the doctrine into one clear whole conception, yet legitimately believe it because apprehension is possible without understanding.

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