Difference between "considered to be" and "considered as"
Is there any difference here between these two sentences? For example: old vines are considered to be expensive. And old vines are considered as expensive.

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Answer

Not a lot of difference but the preposition means that it will be used in different ways. 
Old vines are considered to be expensive. Correct and common English.

To be "considered as" something, the "as" implies/infers that there is a comparison. Eg. in some circles (groups of people) such behaviour is considered as good enough.

Answer

Not sure that I would use "considered as".
... are considered expensive. (maybe) :)