Both "kneel" and "kneel down" refer, or at least can refer, to the physical gesture. "I had to kneel to reach under the sofa". To "go down on bended knee" always refers to a symbolic gesture, whoch may be physical, but more often is purely metaphorical. The phrase may be used making an for an earnest and urgent request, often a form of begging. It may also be used to indicate acknowledging someone's superiority with a gesture of submission. In particular, it can refer to the gesture which was used during the fudal period to swear oaths of fealty, and is still used in some such cedremonies in the United Kingdom when swearing fealty to the King or Queen. It can also be used to the traditional (and now rather uncommon) gesture used during a formal proposal of marriage.
Some definitiosn and related links:
Some examples of use of this phrase:
- We beg the government on bended knees not to cut this budget.
- I propose wooing her before, metaphorically, going down on bended knee.
- The TV network begged her on bended knee to return to the program.
- We have to remain strong in the eyes of the world. We cannot beg on bended knee for help from our allies.
- Do what you like, but don't come to me on bended knee looking for help when things go wrong.
- Do you expect me to come to you on bended knee and ask you for forgiveness?
- The suitors came on bended knee and begged the attention of the princess.
- Film-makers are having to go on bended knee to funders.
- He begged them on bended knee to cross the river so that both armies could fight side by side.
- Imagine Treasury Secretary Hank Paulson down on bended knee before House Speaker Nancy Pelosi. He's begging for his $700 billion bailout.
The Free Dictionary entry says:
Bended was the original past participle of bend, but in Middle English it was superseded in general use by bent. It is now archaic and survives only in this phrase.
and I agree.
I have seen "on bended knee" more often in connection with a gesture of submission, supplication, or respect, and less often in connection with a marriage proposal. It can mean any of these.