Milton! thou should'st be living at this hour. The literary device used in the line above is _________

The literary device used in the line above is an apostrophe. An apostrophe is a figure of speech in which a speaker addresses an absent person, an abstract quality, or a thing as if it were present and capable of understanding. In this line, the speaker addresses the poet John Milton as if he were present and speaks directly to him. This creates a sense of intimacy and immediacy between the speaker and the poet, and helps to convey the speaker's thoughts and emotions.