Sometimes, instead of saying "could/can" or "would/will" (the two most common I've heard), some people say "could/can do" or "would/will do".

Instead of:

> 
> I don't know if it *can*.
> 
> 
> 

I sometimes (but uncommonly) hear:

> 
> I don't know if it *can* do.
> 
> 
> 

Say them with a mild emphasis on the italicized *can* and you'll be saying it as I hear it.

As this is a little hard to express to someone who has never come across it before, I hope someone who sees this knows what I mean. Why is that extra "do" sometimes used?

***Additional note:*** Here are three examples that in jwpat7's opinion may be similar to or represent what Daniel δ refers to:

> 
> I have never crossed the Himalayas, though I might have done. - [Christopher Hughes](https://www.google.com/search?q=%22I%20might%20have%20done%22&tbs=bks:1,cdr:1,cd_min:1969,cd_max:2008&lr=lang_en#q=%22I+might+have+done%22&hl=en&lr=lang_en&tbs=cdr:1,cd_min:1969,cd_max:2008,lr:lang_1en&tbm=bks&ei=nbMLT8_-EaKmiQLd0bD8Aw&start=10&sa=N&bav=on.2,or.r_gc.r_pw.,cf.osb&fp=91f960342228ac50&biw=906&bih=532), 2006
> 
> 
> ...when I could get a vote for Mr. Charlesworth, I did do. ... I made no regular canvass, [but] where I could get a vote, I did do. - [Slade testimony](http://books.google.com/books?id=SNESAAAAYAAJ&pg=PA275&dq=%22I+did+do%22&hl=en&sa=X&ei=8ckLT5f6JYeqiQLQ8_GcBA&ved=0CEYQ6AEwAQ#v=onepage&q=%22I%20did%20do%22&f=false), 13487-8, 1860
> 
> 
> "... When needed I will turn myself in too. And if I can do, you can do too!" - [Oblivion in Progress](http://books.google.com/books?id=RPAHVyyduB0C&pg=PA67&dq=%22and+if+I+can+do+you+can+do+too%22&hl=en&sa=X&ei=6YYMT6nKFIP-iQK24bzzAw&ved=0CDUQ6AEwAA#v=onepage&q=%22and%20if%20I%20can%20do%20you%20can%20do%20too%22&f=false), 2011, pp. 67-68
> 
> 
>