Alfred North Whitehead's first book as a professor of philosophy at Harvard University, Science and the Modern World, is not only a historical treatment of the rise and fall of scientific materialism. It also marks his turn to metaphysics in search of an alternative cosmological scheme that would replace matter in motion with organic process as that which is generic in Nature. Among the metaphysical innovations introduced in this book are the somewhat enigmatic “eternal objects.” The publication of the first (...) and second volumes of Whitehead's Harvard Lectures on the philosophical presuppositions (HL1) and general metaphysical problems (HL2) of science provides students of his corpus with an opportunity to catch the thinker in the act of creating his concepts. In searching through student notes for glimpses of what Whitehead really meant, I have kept in mind his admonition that “no thinker thinks twice” (PR 29). Whitehead never ceased philosophizing, and surely he intended for us to continue thinking with but beyond the letter of his ideas. In this spirit and in light of HL1 and HL2, this article seeks to elucidate the role of eternal objects as a category of existence in Whitehead's Philosophy of Organism, with the goal not simply of textual exegesis, but of showing how the meaning of the fifth category of existence (as he refers to eternal objects in PR) is exemplified in the gradual ingression of the idea in Whitehead's imagination. My aim is to sustain the effort at constructive thought he began, making his speculative hypothesis as explicit as possible so as to better prepare it for critical improvement (PR xiv). (shrink)