What, then, is the difference between saying one can’t “travel both” roads and saying one can’t “travel both / And be one traveler”? And why does Frost think that difference worth preserving? One way to address these questions is to think about what the speaker is actually suggesting he’s “sorry” about. He isn’t, for instance, sorry that he won’t see what’s at the end of each road. (If he were, it would make more sense to use the modified version above.) Rather, he’s sorry he lacks the capability to see what’s at the end of each road—he’s objecting not to the outcome of the principle that you can’t be two places at once, but to the principle itself. He’s resisting the idea of a universe in which his selfhood is limited, in part by being subject to choices. (Compare this to the case of a person who regrets that he can’t travel through time not because he wishes he could, say, attend the premiere of Hamlet, but simply because he wants to experience time travel.)

This assumes, of course, that the speaker regrets that he can’t travel both roads simultaneously. But what if he instead means that it would be impossible to “travel both / And be one traveler” even if he returned later to take the second road? As Robert Faggen puts it, the suggestion here is that “experience alters the traveler”: The act of choosing changes the person making the choice. This point will be quietly reinforced two stanzas later, when the speaker says that “knowing how way leads on to way, / I doubted if I should ever come back”—the doubt is not only that he might return again to the same physical spot, but that he could return to the crossroads as the same person, the same “I,” who left it. This reading of the poem is subtly different from, and bolder than, the idea that existence is merely subject to the need to make decisions. If we can’t persist unchanged through any one choice, then every choice becomes a matter of existential significance—after all, we aren’t merely deciding to go left or right; we’re transforming our very selves. At the same time, however, if each choice changes the self, then at some point the “self” in question becomes nothing more than a series of accumulated actions, many of them extremely minor. Frost’s peculiar addition—“And be one traveler”—consequently both elevates and reduces the idea of the chooser while at the same time both elevating and reducing the choice. The thaumatrope spins, the roads blur and merge.

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