See in text (Hope Is the Thing with Feathers)
When a noun is first introduced, English speakers often use the indefinite article, “a” or “an,” before the noun. This signals that it is one of many and allows the speaker to define it momentarily. Dickinson’s speaker instead uses the definite article, “the,” here to clearly state that hope is the only thing that can perform these functions. This not only strengthens the speaker’s claim, but it also sharpens the focus of the work.