An Essay in Aid of a Grammar of Assent was published by Burns, Oates, and Co. in 1870. Newman worked on it intermittently for twenty years — it is his most difficult book, his most purely philosophical, and his most original contribution to epistemology. The central question: how do human beings arrive at certainty about matters (including religious faith) that cannot be demonstrated with mathematical proof?
Newman distinguishes between two kinds of mental assent: “notional” assent (agreement with an abstract proposition — “God exists” as an intellectual position) and “real” assent (concrete, imaginative engagement with a truth that shapes one’s entire life — “God exists” as a lived reality that determines how one acts, loves, and dies). The difference is not between true and false but between alive and inert — between beliefs that remain in the head and beliefs that inhabit the whole person.
The book’s most original concept is the “illative sense” — Newman’s term for the faculty by which we make the final leap from accumulated evidence to certain conclusion. In formal logic, this leap cannot be justified (no number of probabilities yields certainty). But in practice, human beings make it constantly — we are certain of things that we cannot formally prove, and this certainty is not irrational but supra-rational: it draws on a lifetime of experience, accumulated judgment, and what Newman calls “antecedent probability.”
The argument has implications far beyond theology: it offers an account of how practical reasoning works in every domain — scientific, moral, aesthetic, and personal — that is more sophisticated than anything formal logic can provide.
Collecting An Essay in Aid of a Grammar of Assent
First edition (Burns, Oates, and Co., London, 1870): Cloth binding.
Market values:
- First edition: $100–$300
- Later 19th-century editions: $30–$80
- Fine copies in original cloth: $150–$400