Repetition as a stylistic device is a direct successor of repetition as an expressive language means, which serves to emphasize certain statements of the speaker, and so possesses considerable emotive force.
It is not only a single word that can be repeated but a word combination and a whole sentence too.
As to the position occupied by the repeated unit in the sentence or utterance, we shall mention four main types, most frequently occurring in English literature:
1) anaphora - the repetition of the first word of several succeeding sentences or clauses (a …, a …, a …)
"I want her to live. I want her to breathe. I want her to aerobicize."
(Weird Science, 1985)
2) epiphora - the repetition of the final word (… a, … a, … a)
"She's safe, just like I promised. She's all set to marry Norrington, just like she promised. And you get to die for her, just like you promised."
(Jack Sparrow, The Pirates of the Caribbean)
3) anadiplosis or catch repetition - the repetition of the same unit (word or phrase) at the end of the preceding and at the beginning of the sentence (…a, a …)
"My conscience hath a thousand several tongues,
And every tongue brings in a several tale,
And every tale condemns me for a villain."
The combination of several catch repetitions produces a chain repetition.
4) framing or ring repetition - the repetition of the same unit at the beginning and at the end of the same sentence (a …, … a).
"Swallow, my sister, O sister swallow"
(Algernon Charles Swinburne, "Itylus")
Stylistic functions of repetition are various and many-sided. Besides emphasizing the most important part of the utterance, rendering the emotions of the speaker or showing his emotive attitude towards the object described, it may play a minor stylistic role, showing the durability of action, and to a lesser degree the emotions following it.
Repetition, deliberately used by the author to better emphasize his sentiments, should not be mixed with pleonasm - an excessive, uneconomic usage of unnecessary, extra words, which shows the inability of the writer to express his ideas in a precise and clear manner.
Morphological repetition, that is the repetition of a morpheme, is to be included into the stylistic means.
e.g. I might as well face facts: good-bye, Susan, good-bye a big car, good-bye a big house, good-bye power, good-bye the silly handsome dreams.