In a recent conversation with a friend, I found myself struggling to convey the hierarchy of good writing, particularly of good science writing — a hierarchy experienced so concretely in the act of reading but inexpressible as soon as one tries to dismantle the magic of enthralling prose. The difference between good writing and great writing is always palpable and rarely articulable, but the stakes are even higher in science writing, where the standards of truth and beauty are such that the precise and the poetic must converge in order to yield both comprehension and enchantment.