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In rhetoric, rhetorical devices are often used as a form of persuasion—and evoking an emotional response is a tool used for this intent. However, these devices can be used for other purposes as well.
In Shakespeare's Hamlet, "will he, nill he" (V.i.16) means " with or without the will of the person concerned" or whether he wants to or not. (It is from this phrase that we get "willy nilly.") There are several devices at work here. The first is repetition, which is used (generally) for the purpose of emphasis—whether the emphasis is placed upon a sound, a word or a phrase. We see it first with the structure of the sentence: "will" and "nill" are both followed by "he." We also have the repetition of sounds, sometimes referred to as "sonic devices." In this first phrase, assonance is employed:
Assonance is the repetition of a similar set of sounds, it is used to emphasize intensity, evil, etc.
While this definition notes "similar sounds," assonance specifically points to the repeated use of the same vowel sound. We can see this with the repetition of the "i" sound in "will" and "nill." However, consonance is also used, with the repetition of the consonant sounds of "ll" found at the end of the words "will" and "nill."
Shakespeare is also using asyndeton, where related phrases are used, but conjunctions that might generally be used to join them are missing. Asyndeton is defined as...
...is a stylistic scheme in which conjunctions are deliberately omitted from a series of related clauses.
Here we see that the repeated structure of the phrasing provides emphasis, which is also the purpose of using repetition of any kind.
These devices are used to emphasize what is being said, in the repetetive sound of the words and the structure of the words joined in "will he, nill he."