Oftentimes when a sentence features an “or,” the sentence is listing alternatives (typically exclusive of each other). In the case of a title, however, the “or” seems to be functioning in a different way.
To help demonstrate what I mean, consider the title of an Eliza Haywood novel, “Love in Excess; or, the Fatal Enquiry.” In this example, these words on either side of the “or” do not come across as options as much as a form of clarification. Both phrases are meant. The “or” here functions more as an augmentation—and, it seems to me, this is (at least almost) always the case in a title.
Also (or perhaps alternatively), the “or” translates into/suggests an “is,” as in “Love in Excess is the Fatal Enquiry.” Or, in a more broad sense, this type of “or” enables a metaphor.
When titles have an “or,” they feel more like a duality than a dichotomy. More like two open doors than a choice between two closed ones. Pleasing parallels hinging on the power of juxtaposition.
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Have you used “or” in your poem titles? Why?