Question: What is the difference between *quite* and *pretty* in the following context:

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> The differences between these concepts are quite complicated.
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> 
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and

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> The differences between these concepts are pretty complicated.
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Answer: 
In many cases, it would be equally or more correct to omit either word and still retain the meaning.

"It is broken" instead of "It is pretty broken"

"It is sore" instead of "It is quite sore" etc etc
one would use pretty in this context so that the speaker liked to talk about the mentioned concepts

i would use quite in this context maybe to hint that the speaker himself would rather not talk about the differences between the concepts in full detail -- which is absolutely understandable, as they apparently a r e "quite complicated".. :-)

hope you accomplish to get message across . good luck