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

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

> 
> The differences between these concepts are pretty complicated.
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> 
>

Answer: 
In the fist sentence **Quite** refers to **Completely**. While in the second sentence **Pretty** refers to **a certain extent**.
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