A presumptuous person, according to The Oxford American Dictionary and Language Guide (1999) is one who is “unduly or overbearingly confident and presuming.”  To presume is to “suppose to be true; take for granted.”  Let me give an example of presumptuousness from one of the textbooks I’ve used for many years.  The book—now in its fourth edition (2003), and reputed to be the most widely used textbook in all of philosophy—is The Elements of Moral Philosophy, by James Rachels (1941-2003).  In the book’s final chapter, Rachels sets out a number of requirements for “a satisfactory moral theory.”  Here is the first requirement (from pages 191-2):

A Modest Conception of Human Beings.  A satisfactory theory would, first of all, be sensitive to the facts about human nature, and it would be appropriately modest about the place of human beings in the scheme of things.  The universe is some 15 billion years old—that is the time elapsed since the “big bang”—and the earth itself was formed about 4.6 billion years ago.  The evolution of life on the planet was a slow process, guided largely by natural selection.  The first humans appeared quite recently.  The extinction of the great dinosaurs 65 million years ago (possibly as the result of a catastrophic collision between the earth and an asteroid) left ecological room for the evolution of the few little mammals that were about, and after 63 or 64 million more years, one line of that evolution finally produced us.  In geological time, we arrived only yesterday.

But no sooner did our ancestors arrive than they began to think of themselves as the most important things in all creation.  Some of them even imagined that the whole universe had been made for their benefit.  Thus, when they began to develop theories of right and wrong, they held that the protection of their own interests had a kind of ultimate and objective value.  The rest of creation, they reasoned, was intended for their use.  We now know better.  We now know that we exist by evolutionary accident, as one species among many, on a small and insignificant world in one little corner of the cosmos.  The details of this picture are revised each year, as more is discovered; but the main outlines seem well established.

Rachels is pretty clearly a Darwinian, as I am.  (He is the author of Created from Animals: The Moral Implications of Darwinism [1991].)  I have no problem with his description of the evolutionary process or with the appropriateness of including such a description in an ethics textbook.  But notice what happens by the middle of the second paragraph. “We now know,” Rachels writes, “that we exist by evolutionary accident.”  The implication is twofold: first, that evolution is not part of a divine plan; and second, that science has demonstrated this.  (The most common contrast with “accidental” is “intentional.”)

But science can’t tell us whether the processes that it discovers are part of a divine plan!  Science, by definition, is in the business of studying the natural world.  Whether there is anything beyond the natural world—a supernatural realm—is outside of its purview.  Notice the ease with which Rachels slides from science to metaphysics, and notice the dogmatism of the expression, “We now know that.”  As if it has been demonstrated that there is no god!  This slide is dismayingly common among scientists such as Richard Dawkins, who might be excused on the ground that they’re philosophically naive.  That a philosopher should make such a slide is shocking.

There are many other examples of presumptuousness in Rachels’s book, some of which I set out in a review in Teaching Philosophy a few years ago.  After much soul-searching, I have decided not to use the book again, despite its merits.  It’s well written, easy for students to understand, and thorough.  Rachels covers the main normative and metaethical theories.  There’s also a companion volume, The Right Thing to Do: Basic Readings in Moral Philosophy (3d ed., 2003), which allows instructors to assign primary sources.  But I finally tired of apologizing to my students for Rachels’s presumptuousness.  (His discussion of natural law, for example, is abominable, and he all but defines ethical egoism out of existence.)  Starting this spring, I’m going back to Fred Feldman’s Introductory Ethics (1978), which I used for the first time 20 years ago.  The book is still in print, even though it has never been revised.  Is there any other subject or field in which a 29-year-old textbook could be used?