In the article “Pound’s ‘Metro’ Hokku: The Evolution of an Image,” Chilton Randolph and Carol Gilbertson argue for the subtle importance of Pound’s choice of punctuation in “In a Station of the Metro” in the context of Pound’s Imagiste and Vorticist aesthetic. They note the significance specifically of Pound’s use, in the final published version, of the the semi-colon rather than a colon at the end of the first line, arguing that this altered format indicates both Pound’s debt to and distinction from the Japanese haiku and moreover embodies an entire unspoken theory of art, that is, Vorticism. Throughout the article Randolph and Gilbertson cite two of Pound’s most illuminating essays on the subject of modern verse, “A Few Dos and Don’ts by an Imagiste” and “Vorticism” to form and reinforce their argument. They mention Pound’s declaration that “the one image poem records the precise instant when a thing outward and objective transforms itself, or darts into a thing inward and subjective” to show that the integrity of the poem as an untreated “relation between ideas” rather than a narrative composition of rhythmic units hinges on the semi-colon, for it “creates a mental leap” by which the reader can physically reenact the darting of the outer image into the inner image in the mind.
They go on to assert that the instability of the semi-colon as opposed to a colon reflects Pound’s theoretical principles and in this way (though his principles are decidedly founded on disjuncture and fragmentation) ground the poem and give its “vorticist dynamic” and its powerful, lasting effectiveness. Thus, most importantly, Gilbertson and Randolph assert, that the formal experimentation embodied with “In a Station of the Metro” traces “not only a struggle with “rhythmic” units or visual appeal, but the difficult evolution of [Pound’s] genuinely modernist poetic.”
Your summary captures a different aspect of the argument than Matthew’s by focusing on the shift from an imagist to a vorticist aesthetic. That a single punctuation mark could reflect such a poetic evolution makes for quite a remarkable argument! You might clarify whether the quote about the “darting” inward is from the imagist or vorticist essays–that would help clarify the argument–as would offer the dates for the revisions and how those tracked Pound’s engagement with (and estrangement from Imagism) and eventual movement to vorticism. Great post overall!