A Mandarin Corner YouTube video describes "3 Things Chinese Like about Foreigners". One sentence from this dialogue is the following:
首先我觉得外国人有时候太过于开放。
Shǒuxiān wǒ juédé wàiguórén yǒu shíhòu tài guòyú kāifàng.
Which I translate (directly) to:
First, I feel foreigners are sometimes too excessively open.
What's confusing me is the use of both:
It seems like one of these is redundant.
Question: Why do both 太 and 过于 occur in this sentence?
I'm going to convert my comments into an answer to offer another POV to the already given answer.
太过于 is a set phrase.
KEY defines:
太过于
too...
and KEY French defines it:
trop...
Perhaps this is similar to English usage of too + overly. It's a phrase we often use in English too. A quick google search gives me results like: too overly complex, too overly dependent and too overly ambitious - seems to be about the same logic.
ICIBA also defines it as:
too much
giving examples:
- She's too protective towards her children; she should let them be more independent.
她对孩子太过于爱护, 她应当给他们更多的独立性.
- Cheese, like oil, makes too much of itself.
乳酪, 如同石油一样, 太过于引人注目了.
- Don't be so quick to judge!
不要太过于武断!
Examples of usage (emphasis is my own):
在搜狗CEO王小川、顺为资本投资合伙人周航和腾讯前CTO张志东圆桌论坛上，对于“科技发展与服务用户”的话题讨论上，周航认为，我们很多时候的焦虑，是太过于关注短期的东西了。
Sina: iOS 12加快淘汰速度，iPhone6确实太过于老旧了！！
而今天，还需要给大家再次强调，如今都已经是3月份了，如果按照苹果的更新速度，很快将会在秋季之前发布最新的iOS 12系统，这无疑会加快淘汰的速度，因为iPhone6太过于老旧了。
味太过于咸
and the kicker:
对有些人来说，改变习惯的确是很难很难的事，因为他们太过于原谅自己，太过于迁就自己，太过于开脱自己，太过于娇纵自己。
价格太高 may refer to something cost too much or unaffordable, and 价格过高/价格过于昂贵 may refer to something unworthy.
太开放 probably means they are too open that you can't take it personally.
过于开放 means they are so open that in some aspect, it may be bad for themselves. The people who are supposedly open may or may not care, but it changes many things that breaks the usually logic of the implied aspect, or assumed common sense, that the opinion of the person who say that about what would usually work may fail in this case.
太过于开放 means it could be too bad for themselves, or it is bad for themselves in too many aspects, or something is much more likely to fail or more difficult to fix.
The 3 terms are more different in the case about prices. One may consider something unaffordable but still want to buy it, where you can't say 过高, and consider something else cheap but still not as useful as how it costs, where it probably invite some discussions if you say 太高. Still, in many cases one can be implied from another, unless the context says otherwise.
In the cases about something like openness, it's not unusual for someone to mix them up completely. 太过于开放 surely does NOT mean "it might be not that bad, but it is at least not for me". Actually, "it is too bad", but without watching the video it's not sure whether "I can't take it, fix it, ignore it or have a workaround" is implied, or whether he even notice this distinction.
This usage is conversational, you wouldn't see it in writing. Unless, of course, the writing is trying for a conversational tone. Presumably the speaker started with "太..." but felt that wasn't strong enough and added the 过于.
Grammatically, there's the difference that 太 is (just) an adverb and 过于 is more like a verb. To represent the sentence in English, you could write something like:
Foreigners are overdoing (过于) being open (开放) way too much (太)
Which isn't exactly correct usage, but does sound like something a young person might say.
I'd like to note that 过于 can't normally be translated as "overdoing", it's just the closest verb in English. The reason I say it's verb-like is because 过 is a verb, and the structure works out like this:
过 (surpass) 于 (compared to)
This structure is inherited from an older stage of Chinese grammar.
In this sentence, the speaker can choose 太过 (overly/ excessively) or 过于(overly/ excessively).
Instead of just pick one adverb, that guy mixed the two together
首先我觉外国人过于开放 and 首先我觉外国人太过开放 express the same meaning for the sentence. No need to write "太过于"
太过于 vs 过于, the extent is different. 太过于 denotes larger extent.
Basically,
过于: overly
太过于: much overly
