Aback is a mostly archaic adverb originally meaning at or on the back. So when someone was taken aback they were caught off guard by something coming from behind. Hence the meaning of the modern idiom, take aback, usually inflected taken aback: surprised or disconcerted. The phrase usually has negative connotations, but it can be positive.
Examples
These writers use taken aback well:
There are Britons in Berlin who get taken aback by the directness of Germans. [BBC News]
We’re often taken aback when a respected governor, political candidate, husband or wife is caught cheating. [NPR]
It was recognizable as self-replicating spam, but still, I was terribly taken aback in that first moment. [Edmonton Journal]
Taken aback should not be confused with take back, which means to retract, to return, or to reclaim. For example, these writers misuse taken back in place of taken aback:
I was taken back by the number of women who showed up when we had our first chapter meeting in April. [Homer Tribune]
He was taken back by the mature crowd’s reaction and soon figured out there would be an audience for a national tour. [Sydney Morning Herald]
Taken back is nonsensical in cases such as these, but some readers might not be bothered by it.
